Preheat oven to 350 degrees F. Spray an 8 x 8 baking dish with cooking spray.
Stir together the oats, brown sugar, baking powder, cinnamon and salt in a large mixing bowl.
In another medium size bowl, whisk together the milk, egg and vanilla. Add the melted butter slowly, whisking constantly.
Pour the milk mixture into the oat mixture. Add apples and stir until combined.
Pour mixture into the prepared baking dish. Top with sliced almonds.
Bake uncovered for 35-40 minutes, until the top is golden brown and the oats have set.
Remove from oven and let cool for 5 minutes. Serve and enjoy!