Preheat oven to 400 degrees F.
Add quick oats, butter, 1 tablespoon Splenda and 1/4 teaspoon cinnamon to a mixing bowl. Stir together.
Peel and chop the granny smith apples. Add them to a mixing bowl with 1 1/2 teaspoons cinnamon, cornstarch, 4 tablespoons granulated Splenda and brown sugar. Stir together.
Spray a 9x9 baking dish with no-stick cooking spray. Add the apple mixture to the bottom, then add the oatmeal mixture on top.
Bake 30 minutes, or until the oats are golden brown.