Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners.
In a bowl, mash the ripe bananas until smooth.
Add melted butter to the bananas and mix well.
In another bowl, whisk together flour, cocoa powder, baking soda, and salt.
Gradually add the dry ingredients to the banana mixture, stirring gently.
Incorporate sugar, eggs, and vanilla extract into the mixture.
Fold in chocolate chips until evenly distributed.
Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full.
Bake for 18-20 minutes or until a toothpick comes out clean.
Allow muffins to cool in the tin for 5 minutes before transferring to a wire rack.