Preheat your oven to 400 degrees.
Pour 1 cup of the spaghetti sauce into the bottom of a 9x13 dish. Layer with half of the frozen ravioli & half of the mozzarella cheese. Layer the other half of the frozen ravioli, remaining cup of spaghetti sauce, & remaining cup of mozzarella cheese over top. Sprinkle with parmesan cheese.
Bake, covered with aluminum foil, for 30 minutes. Remove tin foil & continue to cook for 10-15 minutes. Sometimes I will turn the oven up to broil at the very end for a minute to brown the top a little bit more, but that's not necessary.