Preheat the oven to 350 degrees. Coat a muffin tin with cooking spray.
Combine the mashed banana and brown sugar together until well combined.
Beat in the oil, eggs, and vanilla until creamy and smooth.
Combine the flour, cocoa powder, baking soda, baking powder, and salt together in a bowl; mix well.
Gradually add the flour mixture to the banana mixture until just combined. Don't over mix! Fold in the chocolate chips.
Evenly distribute the muffin batter into the muffin tin.
Add a few more chocolate chips and a sprinkling of turbinado sugar over each muffin.
Place into the oven and bake for 15-17 minutes, or until a wooden tester inserted in the center comes out clean.
Remove from the oven and allow to cool for 10 minutes before removing them from the pan to a wire rack to continue cooling.