In a large bowl combine soup and water; add 1 cup of chow mein noodles, onion, pepper, tuna and celery; toss lightly. Turn mixture into 10x6x2-inch or 8x8x2-inch baking dish. Sprinkle remaining 1 cup chow mein noodles over top. Bake in 375° oven 30 minutes.
This tuna casserole with chow mein noodles makes 4 servings.