Dice and brown chicken breast in butter until cooked. Cook rice. Add sauce, black beans and tomato paste to pan of cooked chicken. Simmer until slightly thickened. Stir in grated cheese. Ladle chicken and sauce over rice and top with additional shredded cheese and sour cream as desired. (You may alternatively stir rice into sauce and combine right away.).
Rice: combine 2 cups white rice and 3 cups water, bring to a light boil. Cover and reduce heat to medium - low. Simmer covered 20 minutes or until all water is absorbed. Fluff with fork.