Saute ground beef and onions until meat is cooked; drain.
Add celery, both soups and warm water. Stir in rice, bean sprouts, soy sauce and pepper.
Turn into 9 x 13-inch casserole dish and bake covered for 30 minutes. Remove cover and bake another 30 minutes, sprinkle chow mein noodles on top in the last 5 minutes of baking.