Saute onion and celery in butter. Once softened, add the tuna with the water.Break up the tuna chunks. Add the cream of mushroom soup, and mix well to incorporate all the ingredients. Lastly, add the red or green pepper, and about 3/4 of the chow mein noodles. Pour all into a greased casserole dish, top with remaining chow mein noodles, and pop into a 350 degrees oven for about 20 minutes, until heated through and bubbly. Enjoy with a tossed salad, and crusty bread.