Preheat oven to 350 degrees F. Spray a 9x9 inch baking dish with nonstick cooking spray.
Arrange peeled and sliced apples in the bottom of the prepared baking dish.
Mix oats, brown sugar, cinnamon, flour and salt together. Add melted butter, and mix until well blended. The mixture will be crumbly.
Spread oatmeal mixture over apples.
Bake until the fruit is fork tender, approximately 35 minutes.