Cook noodles according to package directions. Drain and set aside.

In a large skillet, cook beef, green pepper and onion over medium heat until meat is no longer pink, breaking it into crumbles; drain. Stir in the spaghetti sauce, mushrooms and Italian seasoning.

In a separate bowl, combine pepperoni and cheeses.

Spray slow cooker with non-stick cooking spray.

Spread 1/3 of the meat sauce in the bottom of the slow cooker. Top with 1/3 of the noodles and 1/3 of the cheese/pepperoni mixture. Repeat layers twice. Press down to compact.

Cover and cook on low for 2-3 hours or until heated through and cheese is melted.