Grease the bottom and sides of a 9x5-inch loaf pan. Line with parchment paper so the paper overhangs the long sides of the pan.
In a medium mixing bowl, whisk together the gluten free flour blend, cocoa powder, baking soda, and salt.
In a large mixing bowl, stir together the mashed bananas, melted butter, and oil until combined. Add the brown sugar, egg, and vanilla and stir until completely combined.
Add the dry ingredients to the wet ingredients and stir until just combined.
Fold in ½ cup of the mini chocolate chips.
Transfer the batter to the prepared pan and smooth the top. Sprinkle the remaining chocolate chips over the top of the batter.
Bake for 55-65 minutes, or until a wooden pick inserted into the middle comes out almost clean. You may have some melted chocolate from the chips, but you don't want wet batter on the pick.
Cool bread in pan on a wire rack for 15 minutes. Use the parchment paper to lift the bread out of the pan and allow to cool completely on a wire rack.
Grease the sides and bottom of the loaf pan, then line with parchment paper so the paper overhangs the long edges of the pan. Doing this will make it easy to remove the loaf from the pan without touching the melted chocolate chips on top.
Be sure to check the bread, with a cake tester or wooden pick, prior to removing it from the oven. Test the bread in the middle of the loaf to ensure the thickest part of the bread is done.