Preheat the oven to 350 degrees Fahrenheit.
Using a stand mixer, fitted with a paddle attachment; mash the bananas in the bowl then mix together brown sugar, granulated sugar on medium-low speed for 30 seconds. Turn the mixer off, using a silicone spatula scrape down the sides of the bowl. Then, add in the egg and vanilla extract. Mix again for 30 seconds.
Then, add in the cocoa powder, all-purpose flour, baking soda, and salt. Mix until combined 30 seconds to 1 minute. Then pour in the 1 cup of semi-sweet chocolate chips.
Spray a loaf pan with cooking spray. Using the silicone spatula, spread the batter into the loaf pan. Sprinkle the 1/2 cup of mini chocolate chips on to the top of banana bread.
Bake for 1 hour and 15 minutes or until toothpick inserted in the middle comes clean.
Remove the banana bread from the oven. Let rest in pan for 30 minutes, then remove to a plate to continue cooling.