Take 1 each medium to large medium to large squash and zucchini and cut into slices. Saute slices with butter and medium-size onion (sliced thin). Drain. Place 1/2 of squash and zucchini in casserole dish.

Cover with a layer of sliced tomatoes. Sprinkle with bread crumbs and Parmesan cheese. Repeat process with remaining squash and zucchini. Cover and bake at 350 degrees for 30 minutes.