01 - Set oven to 350°F and line a 12-cup muffin tin with paper liners or grease lightly.
02 - In a large bowl, whisk together mashed bananas, eggs, vegetable oil, granulated sugar, brown sugar, and vanilla extract until smooth.
03 - Sift together flour, cocoa powder, baking soda, baking powder, and salt in a separate bowl.
04 - Gently fold the dry ingredients into the wet mixture using a spatula until just combined; avoid overmixing.
05 - Fold in most of the chocolate chips, reserving some to sprinkle on top of the batter.
06 - Distribute batter evenly among muffin cups, filling each about three-quarters full, then top with reserved chocolate chips.
07 - Bake for 18 to 22 minutes, until a toothpick inserted in the center emerges with a few moist crumbs.
08 - Let muffins rest in the tin for 5 minutes before transferring to a wire rack to cool completely.