Cook noodles as directed on package.
Brown ground beef with onion until the meat is no longer pink. Add spaghetti sauce and mushrooms to meat.
Spray large crock pot with cooking spray.
Place layers in crock pots as follows: 1/3 meat-sauce mixture, 1/3 of the egg noodles, 1/3 of the pepperoni/Canadian bacon slices, 1 cup cheddar cheese, 1 cup mozzarella cheese and then repeat these layers twice more.
Cook on low until heated through (approximately 3-4 hours)