Gather all the ingredients for your mug cake.
Combine mashed banana, flour, baking powder, maple syrup, and milk in a 12 oz mug.
Whisk until batter is uniform.
Stir in walnuts and half of chocolate chips.
Air fry at 350ºF for 6-8 minutes or until the center is set.
Sprinkle remaining chocolate chips on top and serve.
