Pizza Pasta Casserole

2 lbs. ground beef
1 large onion, chopped
2 jars (28 oz each)
spaghetti sauce
1 package (16 oz) spiral pasta, cooked and drained
4 cups (16 oz) shredded mozzarella cheese
8 oz sliced pepperoni

In a large skillet, cook beef and onion until meat is no longer pink; drain. Stir in spaghetti sauce and pasta. Transfer to two greased 9 x 13 baking dishes. Sprinkle with cheese. Arrange pepperoni over the top. Cover and freeze one casserole for up to 3 months. Bake the second casserole, uncovered, at 350° for 25-30 minutes or until heated through.To use the frozen casserole, thaw in the refrigerator overnight. Bake at 350° for 35-40 minutes or until heated through.