Gather all ingredients. Preheat the oven to 350 degrees F (175 degrees C). Line a 12-cup muffin tin with paper liners.

Combine flour, cocoa, baking powder, baking soda, and salt together in a large bowl.

Whisk sugar, oil, milk, egg, and vanilla together in a separate bowl until smooth.

Stir egg mixture into flour mixture until just moistened. Fold in bananas and chocolate chips until incorporated.

Divide batter among the prepared muffin cups, filling each about 3/4 full.

Bake in the preheated oven until a toothpick inserted into the center of a muffin comes out clean, 20 to 25 minutes.