Preheat oven to 350 degrees. Spray an 8x8 baking dish with cooking spray.
In a large bowl, combine the oats, brown sugar, cinnamon, baking powder and salt.
In a separated bowl, whisk together the milk, applesauce, butter, egg whites and vanilla.
Pour the wet ingredients into the bowl of dry ingredients. Stir until combined. Add the diced apple to the mixture, and gently stir.
Pour the mixture into the prepared baking dish.
Bake for 20 to 30 minutes (my oven takes 30 min), or until the oatmeal is golden and set. Remove from oven. Cut into squares and serve warm.
Enjoy!