Preheat the oven to 375°F and spray 8-inch square baking dish with cooking spray.
In a large bowl, mix together the oats, baking powder, cinnamon, and salt.
Add in the milk, maple syrup, egg, coconut oil, vanilla and bananas. Stir well to combine. Gently fold in 1 cup of blueberries.
Carefully pour oatmeal mixture into the prepared baking dish. Scatter the remaining blueberries across the top.
Bake for 40 to 55 minutes or until the middle of the bake is set and the top is golden. Remove from the oven and let cool for a few minutes. Portion and serve. Top with additional fresh blueberries and nut butter, if using. Drizzle each portion with maple syrup if you want it a bit sweeter.
Store in the refrigerator in an airtight container for up to 5 days.
To reheat the whole baked oatmeal, cover with foil and reheat in a 350°F oven for about 20 minutes. For individual portions, set oven (or toaster oven) to 350°F and bake for 5-10 minutes or reheat in the microwave for 1 minute.