Preheat oven to 350 degrees F. Grease an 8x8 baking dish.
In a large mixing bowl, combine the following ingredients for the base: mashed banana, maple syrup, applesauce, coconut oil, and vanilla extract.
Add the oats, powdered peanut butter, and salt (for the base) to the bowl, and stir well.
Press the base into the greased baking dish, and bake at 350 degrees F for 10 minutes.
Meanwhile, mix all the ingredients for the topping: oats, chia seeds, cinnamon, sliced apples, maple syrup, and lemon juice.
When the base is done baking, add the topping and press down into base. Bake for an additional 15 minutes.
Remove from oven, let cool in the baking dish, and cut into 9 squares. If desired, serve with a scoop of vanilla yogurt (Greek or vegan). Store leftovers in the fridge.