Place chicken in a 5 quart slow cooker. Combine the tomatoes , 3/4 cup water, onion, bouillon and seasonings; pour over chicken.
Cover and cook on low for 3-4 hours or until a meat thermometer inserted into the chicken reads 170 degrees.
Transfer chicken to a serving platter; keep warm. Pour cooking juices into a small saucepan. Combine cornstarch and remaining water until smooth; stir into cooking juices. Bring to a boil. Cook and stir for 2 minutes or until thickened. Serve with chicken and rice.