Baked Zucchini Gratin Recipe

In a lightly greased 2-quart baking dish, layer onion and zucchini. Drizzle with 1/4 c. butter; sprinkle with mozzarella cheese. In a separate bowl, combine remaining butter, bread crumbs and Parmesan cheese. Sprinkle crumb mixture evenly over the top. Bake, uncovered, at 350° for 35-40 minutes or until zucchini is tender.