1. Combine butter, salt, pepper, onion powder in a small bowl. Core green cabbage, carving out a good-size cavity. Stuff seasoned butter into cabbage cavity, then generously wrap cabbage in heavy-duty foil. Put cabbage, cored end up, on top rack of grill, close lid, and smoke until soft, 2-4 hours. Unwrap cabbage and discard any blackened leaves. Cut cabbage into wedges.