Preheat your oven to 350°F and line a 9×9-inch baking dish with parchment paper. You can also use an 8×8-inch pan, but the baking time may vary slightly.
In a large mixing bowl, combine the mashed banana, nut butter, and non-dairy milk. Stir until the mixture is smooth and creamy.
Add the oat flour, rolled oats, cinnamon, and baking powder to the wet ingredients. Mix until well incorporated.
Gently fold in the dark chocolate chips or cacao nibs. Be careful not to overmix.
Transfer the batter into the prepared baking dish, spreading it evenly with a spatula.
Bake for 25 minutes, or until the top is firm and lightly golden. To check doneness, insert a toothpick into the center—if it comes out clean, your bars are ready!
Allow the bars to cool completely before slicing them into 6–9 portions. Enjoy immediately, or store for later.