Preheat your oven to 350°F (175°C). Grease a 9×9-inch square baking pan and set aside.
In a large bowl, combine the mashed bananas and peanut butter. Stir in the vanilla extract, maple syrup, and egg. Add the milk and mix well.
Small overripe bananas,¼ cup creamy peanut butter,1 teaspoon vanilla extract,¼ cup pure maple syrup,1 large egg,¾ cup whole milk
Add the rolled oats, baking powder, sea salt, ground cinnamon, and nutmeg to the wet ingredients. Stir until the batter is uniform throughout.
Pour the mixture into the prepared baking dish. Top with chocolate chips Bake for 25 minutes, or until the top slightly springs back when touched and the edges are just barely brown
If desired, drizzle the top with additional peanut butter. Let cool slightly before cutting into squares. Serve warm or cold. Store in the refrigerator and reheat in the microwave if desired.