Preheat oven to 350 degrees F. Grease an 8×8″ pan with coconut oil and set aside.
In a large mixing bowl, combine mashed bananas and brown sugar. Stir until sugar is dissolved. (I did all this by hand, but you can use a stand mixer if you want.)
Add oil, egg, and vanilla extract, stirring to combine.
Add flour, cocoa powder, baking soda, and salt to banana mixture and stir until incorporated. Add chocolate chips and pour into prepared pan.
Sprinkle mini chocolate chips on top and bake for 25-30 minutes.
