1 1/2 lbs. ground beef
1 onion, chopped
1 (8 oz.) pkg. twist macaroni, cooked & drained
1 lg. jar spaghetti sauce
6 oz. shredded Mozzarella cheese
1 (3 1/2 oz.) pkg. sliced pepperoni

Brown beef and saute onion. Add sauce. Combine beef mixture and cooked macaroni. In a large casserole dish, layer beef macaroni mixture, cheese and pepperoni until all is used. Bake at 375 degrees for 20 minutes.