Grease bottom and sides of casserole dish (any size desired) with butter. Slice unpeeled zucchini and make a layer on bottom of dish. Add layer of thinly sliced onion, then layer of thinly sliced tomato. Add salt and pepper to taste as you make layers. Repeat all layers again. Cover with foil and bake 25 minutes at 375 degrees. Remove foil, cover with grated cheese. Return to oven until cheese melts.