Your plumber was a hack moron. Now it's doubtful a remodel escutcheon will cover his mistake.

Really? How should he have done it? It had two  temperature knobs before and we didn't want them. We just wanted one.

Also, never expected one of those plates to cover it, as it was completely changed.

We just had this done in two bathrooms. Plumber drilled the tile to fit the new pieces and we opened the wall behind to do the install. Then we used an escutcheon plate that covered the old holes for the handle instead of the trim piece that came with the shower.

In this bathroom we had to pull the vanity top and drawer cabinet to get to the back. This is the backside of the above shower.

That makes sense. Thing is, that's obviously not an option now. What do I need them to do?

Also, I should have mentioned we want to have different tile around the fixture anyway, so tile needed to be removed. Maybe not like this, but it's what we got.

Wow... okay. So yeah, I'd be pissed.

This will be a tough fix.

You have what appears to be plaster or cement over expanded metal lath.

you will need to get some clean tile edges and repair the hole itself with hardibacker attached to some wood nailers. You need to provide support for that valve also.

The trick will be to get the depth of the backer board right so you can thinset the new tiles in place and have them be flush. It won't be easy.

If you are going to be a stickler for how it looks, you could be in for a demo to studs and new backer / tile.

From what I've been told: I don't remember what it is called but there is special drywall like material made to go in tub/shower surrounds, underneath tile, that is meant to be waterproof. That is what you need to be sure your repairman uses, and that he seals the joints correctly. Then he should coat it all (including screw heads) with paint on waterproofing membrane - 2 coats, I've been told, and drying thoroughly between coats. Then he proceeds to apply thinset and tile.

You have the old lath and plaster here and I notice no plastic or tar paper behind it. You have access from behind so I wonder why there's such a big hole in front. To patch I would use cement board. You'll have to screw it to structure on all the edges and probably add a some structure behind it and then tape the edges and cover them with thinset and make sure everything is flat before retiling. I would not worry about waterproofing as you entire wall is not waterproof, but it's probably been working ok like that for a long time.

You could do a temporary fix that may work for awhile. But your long term plan should be to retire the whole thing within a year or two. Providing the patch is at least temporarily watertight. Your handyman really messed up the tile, probably beyond even a temporary repair.

It should say “retile”. But retire would be appropriate, too.