Preheat oven to 350°F.Place sliced peaches in an 8x8" baking pan. Sprinkle with the sugar cinnamon mixture, if using.In a small bowl, combine the cake mix and butter. Sprinkle the crumbled mixture evenly over the peaches and bake for 35-40 minutes or until the fruit is bubbling and the top is golden brown.Serve with ice cream or whipped topping, if desired.