In a 4- or 5-qt. slow cooker, combine chicken, broccoli, carrots, water chestnuts and garlic. In a large bowl, mix next 7 ingredients; pour over chicken mixture. Cook, covered, on low until chicken and broccoli are tender, 3-4 hours., Remove chicken and vegetables; keep warm. Strain cooking juices into a small saucepan; skim fat. Bring juices to a boil. In a small bowl, mix cornstarch and water until smooth; stir into cooking juices. Return to a boil; cook and stir until thickened, 1-2 minutes. Serve with chicken, vegetables and hot cooked rice., Freeze option: Place chicken and vegetables in freezer containers; top with sauce. Cool and freeze. To use, partially thaw in refrigerator overnight. Microwave, covered, on high in a microwave-safe dish until heated through, stirring gently; add broth or water if necessary.