Cook spaghetti according to package directions. Meanwhile, in a large skillet, cook the beef, onion and pepper over medium heat until meat is no longer pink; drain. Add the spaghetti sauce, mushrooms and olives. Drain spaghetti; add to skillet.
Transfer to a greased 13-in. x 9-in. baking dish. Sprinkle with 1 cup cheddar cheese. In a small bowl, combine the soup, Alfredo sauce and Parmesan cheese; spread over cheddar cheese. In another bowl, combine cornflake crumbs and remaining cheddar cheese; sprinkle over the top.
Bake, uncovered, at 350° for 30 minutes or until bubbly and cheese is melted. Let stand for 5 minutes before serving.