Spray one 9x13 pan and one 8x8 pan with cooking spray.
Arrange half the apples in the 9x13 pan and the other half in the 8x8 pan. Sprinkle each with 1/2 cup sugar. Depending on what kind of apples I use, I use less sugar if I didn't use tart apples.
Mix together brown sugar, flour, oats, cinnamon, nutmeg, ginger and butter. Stir until moist. Sprinkle half the mixture of the 9x13 pan. Top oat mixture with about 1/4 to 1/2 cup carmel sauce.
Bake both pans for 20 minutes. Remove from oven.
Take the apples from the 8x8 pan, and arrange them on the 9x13 pan (this makes the second layer). Top with remaining oat mixture and about 1/4 to 1/2 cup carmel sauce. Bake an additional 20 minutes or until apples are tender and top is crisp. Let sit until warm. Serve with vanilla ice cream or whipped topping.