Preheat the oven to 350°F (175°C). Lightly grease an 8-inch (20 cm) or 9-inch (22 cm)loaf pan and line it with parchment paper, leaving an overhang for easy removal.
In a bowl, combine the milk and vinegar and let it sit for 10 minutes until slightly curdled.
Add the sugar and oil to the curdled milk and whisk until the sugar dissolves, then mix in the mashed bananas until well combined.
In a separate bowl, combine the flour, cocoa powder, baking powder and baking soda. Gradually fold the dry ingredients into the wet mixture until fully combined and the batter is smooth.
Gently fold in the chocolate chips.
Pour the batter into the prepared loaf pan and score the top with a small knife about 1/4 inch deep to help the bread rise evenly. Bake for 45 minutes, or until a skewer inserted into the center comes out clean.
Let the bread cool in the pan for 30 minutes to 1 hour before transferring it to a cooling rack. Slice and enjoy! Store in an airtight container for 2–3 days at room temperature or up to 5 days in the fridge.