Preheat grill to medium-high heat. Cut peaches into slices and remove pit. In a bowl, combine brown sugar and cinnamon. Brush peaches with butter and sprinkle sugar and cinnamon over top. Place on grill and cook until grill marks appear, usually 3-4 minutes per side. Try using a grill mat for easy handling and clean up. Makes for a great dessert when combined with whipped cream or vanilla ice cream!