Talk to the players.

The party isn't doing anything wrong per se. Proper use of chokepoints is in fact good tactics, especially if they don't have a strong need to move in and surround the enemy. (If they had a bunch of melee guys getting screwed over by the tactic, then it would stink.)

But the easiest thing might be to talk to the players. Acknowledge that they've done nothing actually wrong but bring up the points you have brought up here, that it's just not very much fun for you, and maybe for them.

Refuse to engage.

To somewhat invert the usual message: "If the party can do it, so can your monsters."

The players like to huddle up in a corridor and refuse to come out? Why would the monsters stand there in the open and try to break through instead of retreating and waiting for the PCs to move?

Encounters as laid out in the book are only the general suggestion of how something works, but unless your monsters are mindless or of merely animal intellect, they should be able to easily recognize the strategy and move to the sides, out of the line of fire of the "nukers" in back. Stalemates aren't fun, especially if there's also some incorporeals or patrolling monster squads hassling the back line (though that depends on the specific fight at hand). Or the monsters could retreat under fire and pull back into their own hallway position.

Too often I see PCs playing with smart tactics while the monsters just growl and run at the party over and over. Only mindless creatures would do that; an obviously overmatched party of intelligent monsters should retreat, regroup, reinforce.

Engage on their own terms.

On the same basic level as above: Anything they can do, you can do. ("Better" is a matter of debate.)

There are very few monsters who totally lack ranged options. If the party likes to huddle in the back and lob spells, arrows, and cantrips, the monsters can absolutely respond in kind. Orcs can throw spears and axes just as well as they can charge in swinging. If the party insists on standing in a tightly clustered hallway position, use their tactic against them. Fireball and lightning bolt can be highly effective against a group that insists on standing in a straight line.

An extended artillery battle might not be much fun, but if they're gonna play games with doorways, you can play right back, and suddenly moving in close seems a lot better.

By the way, keep in mind that you can take an action at any point during a move, so it's completely valid to have a lich standing to one side of the door, out of easy line-of-sight, then run into view, fire a spell off, and move back into cover on the other side of the doorway. They can ready attacks to hit him when he appears, but it's not a foolproof plan since there's also spells like invisibility and mirror image out there.

Spread out the monsters.

Both tactically and strategically. If the party is relying on throwing area effects, make sure you keep your monsters spread out so only a few can be affected at a time, and maybe break up a big fight into a few smaller fights where they'll have to blow through more spell slots if they want to keep doing their shtick. And along that line...

Don't let the party rest easy.

This strategy seems to me to be very spell-slot-intensive. They have to keep the front line healed, and get almost all their damage from big damage spells like fireball. That suggests to me that the party may be sleeping more than normal, and that you might be allowing them to go take a long rest any time they want to.

Pressure the party to hurry up with time sensitive missions. Launch ambushes if they sleep in the dungeon. If they leave the dungeon to rest, the monsters use that time to reinforce their numbers, reinhabit rooms previously cleared, set guards or traps, block doors or build barricades, summon demonic defenders, and so on. Make the monsters at least as tactically smart as the PCs are. Let the party know that relying almost entirely on the spellcasters' damage output is not going to cut it.

The module is only a suggestion.

The module should not be treated as a bible. Encounters can and should move around, DMs are encouraged to add or remove creatures to make the fights harder or easier, and so on. Tune your adventure to the party, if necessary. Don't feel constrained by the words on the page.

If they're depending heavily on spells for damage, counter magic with magic when you can, especially if they keep leaving the dungeon to "wait until tomorrow".

The local spellcasters can and should adapt to their strategies by preparing protection from elements, wall spells, even globe of invulnerability if the levels are high enough. Keep in mind that a simple fog cloud can be utterly devastating to any ranged combat tactics, and a wall of fire blocks line of sight in addition to pulsing fire damage onto the party and forcing them to either back off or run through.

Your players are not choosing to fight from doorway choke points. You are.

"Yeah, you have 4 undead zombies, 2 living suits of armor, and a weakened Lich looking at you once you open the door. Roll initiative!"

All of your monsters are just standing in plain view in the middle of a well lit and empty room waiting for hapless adventurers to come along and harvest some XP from them? That's not even good video game design and RPGs should be much better than that.

Immerse the party in the story. Describe to the party what they are seeing. There's a large room with toppled and broken furniture pushed against the walls. There is a dusty and faded tapestry hanging from the ceiling over one corner of the room. There is a glint of metal from some pieces of armor laying on the floor near the furniture. Then put 2 of the zombies in a darkened corner behind behind the tapestry where they are not immediately visible and the other 2 at the back of the room or under some debris so they attack from a different angle. Let the party think the armor is some treasure to grab and have them come to life when any of the party approaches them. Draw them into the room and let them find the monsters in a more realistic manner. Have the lich reveal itself once the battle has begun.

It takes thought and planning by the DM but it makes for a much better game.

Talk to the players

They might see using a clever strategy as good play, or they might be bored with the situation. Discuss solutions.

Sometimes camping should work

Against mindless enemies the strategy should simply work. If playing it out would not be fun or would take too much time (ask the players!), eyeball how much resoruces the fight should take and ask if the players are fine with losing that many hit points / spell slots / items / hit dice if you declare all the enemies dead with that. If the players are not fine with this, play it out and learn to make better estimates. Or maybe they enjoy they occasionaly show of power; that is fine, too.

The strategy gives initiative to the enemy

Typically, player characters are invading a location that houses superior forces and they rely on taking them one convenient encounter at a time. The strategy of staying in a corridor and killing things gives the enemy the initiative - the enemy can usually retreat, refuse to engage, and, if they are not in a dead end, get reinforcements. If players used plenty of magic or other consumables, retreat and come back when the spells are done. Retreat in case of another salvo of consumable resources.

Play the enemies as smartly as they deserve. Being hit on both sides will make the tunnel a lot less convenient, as will being targeted from afar by archers that one cannot see. Or maybe the enemies will get their own tanks.

If the players are not used to enemies that act with strategy, or if them losing is not a possible outcome of play, either discuss this matter out of character or let the characters make intelligence checks to figure out this downside of the strategy (with advantage to fighters and soldiers), or maybe have a cocky boss declare what they are going to do while the characters are camping in the corridor.

Also remember random encounters

A typical way of representing patrols, roaming creatures and the attention caused by noise is random encounters. Some modern dungeons might have neglected them, but if it makes sense for the location, consider writing a random encounter table and checking it on fixed intervals and when there is noise. The monsters should not arrive immediately, but camping in a corridor is a fine way of spending time.

How effective is it to fight from a corridor, really?

Consider issues of vision for the characters who are farther in the corridor. Their allies are in front, and, furthermore, the sides of the corridor restrict their field of vision significantly. Take this into account and and give out disadvantage or restrict field of vision as necessary. Especially consider size differences, such as smaller or shorter characters behind bigger ones. This need not be a matter of size category only.

Suggest scouting and give information

It is often a bad idea to charge into an unknown room. It might contain traps and other nasty surprises. Allow knowledge-type rolls and suggest scouting for the players to have some information about what lies ahea; if it turns out that the room has interesting and useful features, they will be more likely to go there once they learn of such features.

Your players are tacticians

I have some players like this, and I reward them with an inspiration if they find a creative way to do anything, including solving puzzle and defeating encounter. But I have one agreement with them: same trick won't work twice.

I explain the reason to them: I enjoy being amused, or even being trolled, by their creative method, but I don't want to watch the same trick getting used again, and again. It'll get old quickly. Find a new one so I don't get bored.

That works! They enjoy finding new tactics, even simple, but clever, ones. It's a win-win situation. So, talk to them not to overuse the trick.

If they are indeed tacticians, use these methods to stop or deter them from overusing the trick (after you talk to them, preferably):

Simulate real world

Objects have hit points, too! A section of stone wall has AC of 17. A dungeon wall should be large and resilient, so have average hit points of 27.

• Throw a fireball or two, or maybe a bomb, and tell them the nearby walls crumbled, and suddenly 5 ft door become 15 ft. Or the walls nearly collapsed, they will get the hint.


• That big orc boss right there doesn't like being stalled. He smashes the walls and creates a new door for his minions to attack the backliner. Add some cool boss line before smashing the wall
  

_{Disclaimer: RAW, fireball doesn't damage objects, but as a DM you can go simulationist (talk to your player) and make it (and other spells) interact with object.}

Shutting door trap

Or any trap. The idea is that you can't stand at the door.

One example is demonstrating that the doors in the dungeon shut themselves automatically.

"... and John, just before you pass through the door, the door is slamming shut. Do you want try to pass through?"

Most of the time they will try just to pass, but if they try to block it from closing, and if they do, they take some damage because it turns out it is unblockable (or very hard to block). They might also get separated, but allow them to join up easily. Over time, they will take the hint and avoid standing at the door.

In addition to the great answers already here, there's another, pretty simple option: Just give the players a reason to want to get into the room, and make the opponents the ones wanting to keep them out of it.

You want to hang back in the hallway? Great. That choke point also means it will only take a small handful of the opponents to hold you off. Meanwhile, the other cultists will go ahead and sacrifice that princess you were sent to rescue; your rivals will get to that powerful artifact first; the villain will escape and seal the only exit behind him; etc.

What enemies?

Just because we know the room is laden with enemies does not mean the players will automatically perceive the enemies. The zombies and armor just look like odd shadows in the room. No one notices until they are already inside the room.

We need to get out of here now!!!

"A flood of rust monsters are charging through the hallway with a baby Tarasque brining up the rear. Maybe we should not wait in the hallway..." Your players can not afford to stay in the hallway and are forced into the room. The reason could be a rolling boulder, a quickly flooding tunnel, a methane gas leak (more fun times ahead with this one), or something else that the players KNOW that they can not handle and need to get moving.

Another fun one: They have shock / blast runes cast on them. If they don't leave before a magically growing field reaches them their shock / blast runes go off and we have a crisp PC.

Leeroy Jenkins

Not the best solution but an NPC that does not wait. Make sure they are important to the players so players don't just BBQ the NPC themselves and have to rush in to help them. ies.

Some ideas:

Use creatures who have powerful ranged attacks that need to "charge up" over a few rounds. The party could plink them, but they'll end up taking a lot more damage than if they rush and disrupt the enemy.

Have your enemies be intelligent enough to also rely on chokepoints, but with the advantage of home-turf knowledge. A narrow corridor makes for a good choke point, but when the enemy knows where the secret passages are, they can sneak behind the party and end up being able to attack from both sides.

Place a pit trap a few feet before the door - your PCs will have to choose between going into the room, or leaving. The monsters will happily stay inside the room, waiting. The PCs can't camp out at the doorway because of the pit.

Many good suggestions already, here's a couple more suggestions to get your players longing for open terrain (listed by preference):

Clever Combat Initiation

Bait- Put something in the room that compels them to enter quickly: a loved one or friend bleeding out, a valuable treasure teetering on the edge of a cliff, the Big Bad fleeing out a door on the far side. These can be illusions to be particularly devious.

Pressure- Put something behind them to compel them to leave the hallway: a sea of minions, a rolling boulder, a slow flood of lava or poisonous fumes.

Traps- While standing outside a door, the ground can give way to a ramp that rolls them into a lower room. After entering due to pressure or bait, a portcullis could fall down trapping them inside. A single player could get pulled or teleported inside, triggering a stone slab door to start slowly closing, forcing the players to abandon their friend or enter quickly.

Cover

Concealment- Enemies can be positioned around corners, up on a domed ceiling, or down in a pit so they cannot be seen from the doorway. Spells like Darkness, Invisibility or illusion magic can help with this.

Protection- Each line of sight obstruction increases the AC of the target. In a case where frontline allies are blocking a doorway and enemies are partially behind the wall that encloses the door, its reasonable for you to give the targets half(+2AC), three-quarter(+5AC) or even full cover(untargetable).

Friendly Fire

Some systems (not 5e) have friendly fire so if shooting targets near or past an ally, if the shooter misses by a certain threshold, they accidentally hit their ally and deal damage to them instead.

Targeting Limitations

Spells often specify that they must target a point they can see. Ranged attacks against unseen/invisible targets have Disadvantage. With all the creatures and fighting happening in such a close chokepoint, its reasonable to say the enemies cannot be targeted in the first place or must be targeted with disadvantage. Alternatively, you could halve the range of weapons or spells being used through such a chokepoint.

Note: Be careful of tricking players too drastically or too often, as this will encourage them to be especially careful and meticulous, inspecting every square foot for traps and illusions, which can turn a 3hr dungeon into a 3 session dungeon crawl.

I believe Thaumaturgy can swing open or slam shut a non magical unlocked door. Having an enemy hold and action to slam the door shut on your party at a key moment could cause a huge problem for the party.

The problem then becomes about asking yourself how many inhabitants are thaumaturges.