Prepare your grill for cooking.
Mix the cabbage, salt, pepper, garlic, mustard powder, chili powder and onion powder together in a mixing bowl. Use your hands to massage it all together.
Transfer to an 8 in square aluminum pan.
Dot with butter and sprinkle with sugar, if using.
Roast on the grill, stirring occasionally, until the cabbage is tender. For me it was 25 minutes.