In a mixing bowl, mash the ripe banana until smooth.
Add the old-fashioned oats, baking powder, and a sprinkle of ground cinnamon into the bowl. Mix them together until well combined.
Pour in the melted coconut oil and milk. Stir until everything is nicely incorporated.
Gently fold in the mini chocolate chips, ensuring they are evenly distributed throughout the dough.
Using your hands or a spatula, shape the dough into a cookie shape and place it in the air fryer basket.
Set your air fryer to 350°F (180°C) and cook for about 10-12 minutes, or until the cookie is golden brown and firm to the touch.
Once cooked, remove the cookie from the air fryer and let it cool for a few minutes before enjoying.