For topping, combine brown sugar, butter, corn syrup, and cinnamon in a small bowl; set aside.
Tear off a 36x18-inch piece of heavy foil. Fold in half to make an 18-inch square. Place apples in the center of the foil square. Drizzle with topping. Bring up opposite foil edges, and seal with a double fold. Fold in remaining edges to completely enclose the apples, leaving space for steam to build up.
Grill for 30 to 35 minutes or until apples are tender. Serve apples warm with ice cream. Makes 4 to 6 servings.