Preheat oven to 375°F. Line a muffin tin with paper liners.

In a large bowl, whisk together flour, cocoa powder, sugar, and baking soda.

In another bowl, combine mashed bananas, eggs, vegetable oil, and vanilla extract. Mix well.

Pour wet ingredients into dry ingredients and stir until just combined. Fold in chocolate chips.

Divide batter evenly among muffin cups. Bake for 20 minutes or until a toothpick inserted into the center comes out clean.

Allow muffins to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.