Divided the potatoes and onions evenly between two sheets of heavy-duty foil (approximately 18 inches square), that have been sprayed with nonstick cooking spray.
In a bowl, add the parmesan cheese, 3/4 cup each of the cheddar and mozzarella cheese; stir to combine.
Sprinkle the cheese mixture over the potatoes.
Sprinkle with bacon, butter cubes, chives, seasoned salt and pepper.
Fold the ends of the foil to make a packet (I bring 2 opposite ends of the foil over the potatoes and fold or roll downward, then I roll the unsealed ends inward toward the filling and give them a good press to seal).
Grill, covered, over medium heat for 35-40 minutes or until potatoes are tender.
Remove from the grill, open carefully, and sprinkle with remaining cheese.