Preheat the oven to 375°F. Grease a square baking pan and set aside.
In a medium bowl, mix together the oats, baking powder and salt.
In a separate bowl, mix together the egg, mashed banana, milk and vanilla until fully combined.
Slowly mix in the wet ingredients into the dry ingredients until fully incorporated. Fold in half of the banana coins.
Pour the oat mixture into the prepared baking pan. Line the top of the baking pan with the remaining banana coins.
Bake in the preheated oven for 25 minutes. Remove from the oven and sprinkle the top with the brown sugar. Return to the oven, and broil for 3-4 minutes.