PLACE meat in slow cooker, cutting into 2 pieces if necessary to fit; top with yellow onions and barbecue sauce. Cover with lid. Cook on LOW 10 to 12 hours (or on HIGH 5 to 6 hours).
REMOVE meat from slow cooker; cut into thin slices. Return to slow cooker; stir gently. Combine coleslaw blend, dressing and green onions.
SERVE meat with coleslaw and rolls on the side. Or fill rolls with meat mixture and coleslaw just before serving.