Mix all ingredients except cornstarch and water in 2- to 3 1/2-quart slow cooker.
Cover and cook on high heat setting 2 to 2 1/2 hours or until vegetables are tender.
Mix cornstarch and water; stir into vegetable mixture.
Cover and cook on high heat setting about 15 minutes or until thickened. Cool about 2 hours.
Spoon relish into container. Cover and store in refrigerator up to 3 weeks.