Place ribs in 3 1/2-to 4-quart slow cooker. Cover with onion slices. Mix hoisin sauce, vinegar, soy sauce, ginger and sesame oil; pour over ribs and onion.
Cover and cook on low heat setting 8 to 10 hours or until ribs are tender. Remove ribs to serving platter; keep warm. Skim fat from surface of juices in cooker. Serve ribs with sauce; sprinkle with cilantro.