Preheat the oven to 350°F and grease a muffin tin generously with cooking spray.
In a large bowl, stir together the oats, baking powder, cinnamon and light brown sugar.
In a separate small bowl, whisk together the mashed banana, milk, eggs, melted butter and vanilla extract. Add the wet ingredients to the bowl with the dry ingredients and mix just until combined. Divide the mixture among the muffin cups, filling them full.
Bake the oatmeal cups for 25 to 30 minutes or until they are golden brown on top. Remove them from the oven and let them cool in the pan for 5 minutes before transferring them to a rack to cool completely.
Top the cooled oatmeal cups with your choice of fresh or dried fruit, chopped nuts, toasted coconut or maple syrup.