In a large bowl, toss potatoes with green onions, bacon, salt and pepper. Place half of the mixture on a greased double thickness of heavy-duty foil (about 18 in. square); dot with 1 tablespoon butter. Fold foil over potato mixture and crimp edges to seal. Repeat to make a second packet.
Grill, covered, over medium heat 20-23 minutes on each side or until potatoes are tender. Remove from grill.
Open foil carefully to allow steam to escape. Sprinkle potatoes with cheese. Grill opened packets, covered, 3-5 minutes longer or until cheese is melted.