Preheat the oven to 350º F (180º C). Grease a loaf pan with no-stick baking spray. I used a 9 x 5 x 3-inch loaf pan. NOTE: Line your loaf pan with parchment paper, letting the excess hang over the long sides to form a sling for an easy unmold process.
Mix flour, cocoa, baking powder, baking soda, and salt in a medium bowl. Set aside.
Stir together milk and vinegar. Let the mixture stand at room temperature for 5 to 10 minutes. When it is ready, the milk will be slightly thickened, and you will see small curdled bits. Set aside.
In a medium bowl, mash the ripe bananas with a fork until completely smooth.
Stir the melted butter, oil, and vanilla extract into the mashed bananas; mix until combined. Add brown sugar; mix to combine. Stir in milk mixture until well incorporated. Stir until smooth.
Stir the dry ingredients into the wet ingredients, don’t overmix. Stir in 3/4 cup of the chocolate chips; mix to distribute evenly.
Pour batter into the prepared loaf pan. Sprinkle the remaining 1/4 cup of chocolate chips over the top of the bread.
Bake for 50-60 minutes, or until a toothpick inserted into the center of the bread comes out mostly clean; you might have some melted chocolate chips on the toothpick, which is fine. NOTE: Since we added chocolate chips to the batter, it might be hard to check for doneness using the toothpick test because you might have some melted chocolate chips on the toothpick. In this case, you can also check by gently pushing the center top of the chocolate banana bread down with your finger. If it feels relatively firm and bounces back when you release your finger, that's a good sign that it's done.
Remove the pan from the oven and set it on a wire cooling rack. Let the bread cool in the pan for 15 minutes. Then, run a knife around the edges of the bread, gently remove the loaf from the pan, and place it on a rack to cool completely. Cut into slices with a serrated bread knife and serve.