Saute zucchini and onion in hot oil in a skillet until tender. Spoon one-third of pasta sauce nto a lightly greased 9-inch square baking dish. Layer with half each of ravioli, zucchini mixture, and mozzarella; top with one-third of sauce. Repeat layers, ending with sauce. Sprinkle with Parmesan cheese.
Bake at 375 degrees 10 minutes or until thoroughly heated.
