Preheat the oven to 350 and lightly coat an 8 x 8 baking dish with cooking spray, butter or oil and set aside.
In a large mixing bowl, add your mashed bananas and cocoa powder and mix very well until a thick, chocolate batter remains. Stir through chocolate chips, if desired, and pour into the greased baking dish. Bake for 20-25 minutes, or until firm on top (the middle will still seem undercooked- This is perfect). Remove from oven and allow to cool completely in the baking dish. Once cooled, refrigerate for an hour or so. Cut into pieces and enjoy!
Brownies are best kept in the refrigerator, especially for the best texture. These are freezer frienfly too.