Step 1: Preheat your grill to medium heat or prepare a bed of hot coals in your campfire.
Step 2: Cut four 12x12 inch squares of heavy-duty aluminum foil.
Step 3: In a medium bowl, combine the sliced apples, brown sugar, cinnamon, nutmeg, and a pinch of salt. Toss well to coat.
Step 4: Divide the apple mixture evenly among the four foil squares, placing the apples in the center.
Step 5: Place one pat of butter (1 tablespoon) on top of the apples in each packet. If using granola, sprinkle it on now.
Step 6: Fold the sides of the foil over the apples and seal tightly by crimping the edges to prevent steam from escaping.
Step 7: Place the packets on the grill or over the hot coals. Cook for 15-20 minutes, or until the apples are tender when pierced with a fork (carefully open a corner to check).
Step 8: Remove from heat and let rest for 5 minutes before serving directly from the foil.