1Spray 5- to 6-quart slow cooker with cooking spray. Place turkey in cooker. Arrange sweet potatoes and onions around turkey. Mix remaining ingredients except cornstarch and water in small bowl; pour over turkey and vegetables.
2Cover and cook on Low heat setting 7 to 8 hours.
3Remove turkey and vegetables from cooker; cover to keep warm. If desired, skim fat from juices in cooker. Pour juices into 4-cup microwavable measuring cup. Mix cornstarch and water in small bowl until smooth; stir into juices in cup. Microwave uncovered on High 2 to 3 minutes, stirring every minute, until mixture thickens. Serve with turkey and vegetables.