Preheat oven to 425 F.
Line standard muffin pan with 12 liners and set aside.
In a medium bowl, mash banana with a fork.
Then beat in the egg and add rolled oats, baking powder, brown sugar and vanilla.
Mix well.
Divide the batter into the prepared muffin pan and bake for 15 minutes.
Remove from oven and cool for 5 minutes.
Remove muffins from pan