1. In a small skillet, saute green pepper and onion in 1 tablespoon butter until crisp-tender; set aside.
2. In a large saucepan, bring the water, rice and remaining butter to a boil. Reduce heat; cover and simmer for 25 minutes or until rice is tender. Stir in the chicken, soup, green beans, water chestnuts, carrot, mayonnaise and green pepper mixture.
3. Transfer to a greased 2-1/2-qt. baking dish. Sprinkle with cheese if desired. Cover and bake at 350° for 35-40 minutes or until heated through. Yield: 6-8 servings.