Preheat oven to 350F degrees. Lightly grease an 8x8 inch baking dish with non stick cooking spray.
Prepare crumb topping: In a medium bowl, combine brown sugar, rolled oats, flour and salt. Mix evenly until combined.
Place the apple mixture in prepared baking dish.
Prepare apple filling mixture: In another bowl, combine apples, granulated sugar, cinnamon and salt. Toss to coat apples evenly.
Sprinkle the prepared crumb topping on top of apples. Bake for about 45 - 50 minutes or until streusel is crispy.
Transfer to cooling rack and let cool for about 20 -25 minutes. Serve with Vanilla ice cream or whipped cream.