1. Preheat the oven to 375 degrees and grease an 8x8 baking dish with nonstick cooking spray.
2. In a large bowl, stir together the mashed banana, brown sugar, eggs, vanilla, baking powder, salt, and cinnamon until well combined.
3. Add the milk and whisk to mix.
4. Stir in the oats.
5. Spread the mixture evenly in the baking dish. Sprinkle the chocolate chips over the top of the oatmeal.
6. Bake for 45 minutes, then remove from oven and allow to cool for at least 15 minutes before serving.