In a bowl, whisk together the first 9 ingredients; stir in tomatoes. Place sweet potatoes in a 5- or 6-qt. slow cooker; top with chicken. Pour tomato mixture over top. Cook, covered, on low until chicken is tender and a thermometer reads 170°, 5-6 hours. , Remove chicken and sweet potatoes; keep warm. Transfer cooking juices to a saucepan. In a small bowl, mix cornstarch and water until smooth; stir into cooking juices. Bring to a boil; cook and stir 1-2 minutes or until thickened. Serve sauce with chicken and potatoes.