Cook mostaccioli according to package directions; drain and set aside.
Brown sausage in a large skillet, stirring until it crumbles; drain well. Stir in mostaccioli, spaghetti sauce and Parmesan cheese; pour into a lightly greased 2 1/2-quart baking dish. Top with mozzarella cheese. Bake at 350°F for 25 minutes or until thoroughly heated.