Put apples in greased 8 inch square baking dish; mix in cinnamon. In a bowl, combine sugar and flour. With pastry blender or 2 knives, cut in margarine and peanut butter until mixture resembles coarse crumbs. Add 1/2 cup to apple mixture, mix well. Sprinkle remainder over apples. Bake uncovered in 375* oven about 40 minutes or until apple is tender and top is lightly browned. Serve warm as is or with ice cream or whipped topping.