Toss apples with 1/4 cup of the brown sugar and 1 tsp of the cinnamon. Spoon into 8- or 9- inch baking dish.
Combine oats, the remaining brown sugar and 1 tsp 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.