Preheat over to 350.
Mix together flour, oats, brown sugar and cinnamon. Cut in butter or margarine. Set aside.
Spread 4 cups sliced apples on bottom of buttered pan (8x8). Sprinkle with sugar (& cinnamon if you like it).
Cover with crumb mixture and pat down lightly.
Bake at 350 for 35-40 minutes and enjoy.