Cut each potato lengthwise into four wedges. Cut away the white part, leaving only ¼ inch on the potato skins. Microwave the skins on high for 10 minutes or until tender.
Mix together the butter, salt, pepper, and rosemary and brush this on both sides of the potato skins.
Grill the potatoes, skin side up and uncovered, for 2 or 3 minutes or until lightly browned. Turn the potatoes and position them over indirect heat.
Grill for two more minutes.
Top with cheese, cover, and grill until the cheese melts. Sprinkle it with onions and sun-dried tomatoes.