Do you mean terra cotta? In any case we owned a poured concrete house once, walls 12” thick solid concrete on exterior. We had a contractor fasten 3/4” plywood to the exterior walls with glue and screws prior to drywall.

Ceramic block or cinder block (basically similar to concrete)? If cinder block, I would most likely use wood strapping or plywood attached with construction adhesive and Tapcon fasteners.

It's ceramic block, not cinder block. They're hollow, and the exteriors aren't that thick, so screws (even tapcons) make them crumble and don't have enough to bite. I also didn't allow in the design sufficient space to fur out 3/4" for a backing, (they butt right up to the door openings on both sides of the U). Though I could always modify a cabinet if necessary, I suppose.

" Though I could always modify a cabinet if necessary, I suppose. "

You will most likely need to do that. Also not certain I would trust plywood or furring with only construction adhesive so that may complicate matters some.

I should say that there's a pretty robust and well-adhered layer of plaster on the inside of the blocks. As in near impossible to chip off. So we've got some general thickness.

Is there a solution using wing nuts that might work?

We have no idea what this ‘ceramic’ block is. I’ve been in the historic preservation trade for thirty years in Maine and Georgia and never heard of it. Can you post photos so we have some better sense? There must be some way of attaching since you must have trim and doors?

Here's a pic I've got of the gutted bathroom. You can see the blocks at the bottom of the wall and on the right, with plaster over top.

Here's another view: close-up of what the bricks look like. Any help?