Preheat oven to 350°F. Lightly grease a 9x5-inch loaf pan with butter or baking spray.
In a large mixing bowl, mash the bananas until smooth. Stir in the brown sugar, egg, melted butter and vanilla extract.
In another bowl, whisk together the flour, cocoa powder, baking powder, baking soda and salt.
Add the dry ingredients to the wet banana mixture and mix until combined. Stir in the chocolate chips.
Pour batter into the prepared loaf pan. Bake for 50 minutes to 1 hour or until a toothpick inserted into center of the loaf comes out clean. Allow bread to cool before serving.
Notes
You can store banana bread at room temperature for 3-5 days or in the freezer for up to 3-4 months.