Toss apples with 1/4 cup of the brown sugar and 1 tsp of cinnamon. Spoon into 8 or 9 inch square baking dish.
Combine oats, the remaining 1/4 cup brown sugar and 1 tsp of cinnamon in medium bowl. Cut in margarine with pastry blender or two knives, until mixture resembles coarse crumbs. Add wafer crumbs; mix well. Spread crumb mixture evenly over apples.
Bake 30 to 35 minutes or until apples are tender. Serve warm or cooled. Top with whipped topping.