I make a chicken parm meatball that I prefer over any other parmigianaa I’ve had.

Oyster mushroom is good if you're talking about the breaded kind.
For the lighter Italian style version, I think zucchini and summer squash are a nice addition to the sliced eggplant.

I’m a dedicated meat eater, but actually prefer vegetarian parmigianas to the meat varieties. I like mushroom best, but tofu is also pretty dang good.

https://www.foodnetwork.com/recipes/giada-de-laurentiis/mushroom-parmesan-recipe-1916978

https://www.allrecipes.com/recipe/13896/tofu-parmigiana/

How do you feel about parmigiana, and what kinds could I try beyond veal, chicken, and eggplant?