Preheat the oven to 350 degrees F. Grease an 8 x 8 square baking dish and set aside.
In a large bowl, mix together the oats, brown sugar, baking powder, salt, and cinnamon. Set aside.
In another small bowl, whisk together the milk, egg, applesauce, and vanilla extract.
Pour the liquid mixture over the oat mixture and stir to combine. Stir in the peanut butter and mix until combined. Add the apples and stir again. Pour mixture into prepared pan.
Bake for 35 minutes or until the top is golden and oatmeal is set. Let cool for 5 minutes and serve warm.
Note-this baked oatmeal is great reheated in the microwave. We like to make a pan and eat it throughout the week. This recipe can easily be doubled for a 9 x 13 pan. Use gluten-free oats to make this recipe gluten-free. You can serve with brown sugar, an extra splash of milk, cinnamon, or raisins if desired!