Cook fettuccine according to package directions. Meanwhile, in a Dutch oven, cook beef and onion over medium heat until meat is no longer pink; drain. Stir in the mushrooms, tomato sauce, pizza sauce, tomato paste, sugar and seasonings. Drain pasta; stir into meat sauce.
Divide half of the mixture between two greased 2-qt. baking dishes; sprinkle each with 1 cup mozzarella cheese. Repeat layers. Top each with pepperoni and Parmesan cheese.
Cover and bake at 350° for 20 minutes. Uncover; bake 10-15 minutes longer or until heated through.