Preheat oven to 375° F. Coat a 13 x 9-inch pan with cooking spray.
In a small bowl, combine brown sugar, flour, oats, margarine, cinnamon, nutmeg, and vanilla. Blend with a fork until moistened (mixture should be crumbly).
Layer apples in a pan and sprinkle brown sugar mixture evenly over top. Bake 30 minutes.