Place sliced apples on a large sheet of foil. About 12 -inches wide.
Sprinkle on brown sugar and cinnamon. Place butter on top of apples and then place another piece of foil on top and wrap up making sure to seal completely.
Place foil pack on indirect heat on the grill. Close grill lid and cook for about 20 minutes.
Carefully remove packet from grill. Pierce a hole in the top to allow steam to escape. Unfold and serve.
Video
Notes
To make in the oven, place foil packet on baking sheet and cook for 20 minutes at 400 degrees F.