Cook noodles according to package directions. Meanwhile, in a large skillet, cook the beef, onion and green pepper over medium heat until meat is no longer pink, breaking the meat into crumbles; drain. Add pizza sauce and mushrooms; heat through. , Drain noodles. In a greased 13x9-in. baking dish, layer half each of the noodles, beef mixture, cheeses and pepperoni. Repeat layers. Cover and bake at 350° for 15-20 minutes or until heated through., Freeze option: Cover and freeze unbaked casserole for up to 3 months. Remove from freezer 30 minutes before baking (do not thaw). Cover and bake at 350° for 45-50 minutes. Uncover; bake 15-20 minutes longer or until heated through.