Preheat oven to 350 degrees F. Grease an 8x8 inch square or 7x11 inch rectangular baking dish.
In a large bowl, mash the bananas. Next, add the milk, peanut butter, egg, vanilla, and maple syrup (if using). Whisk to combine.
Next, add the rolled oats, baking powder, cinnamon and salt. Stir to combine.
Transfer the oatmeal mixture to the prepared baking dish. Spread evenly with a spatula.
Place in oven and bake for 35-40 minutes or until inserted toothpick comes out clean.
To serve, top with a drizzle of peanut butter and additional banana slices, if desired.