Preheat oven to 350 degrees.
In a large bowl, combine the melted butter and sugar until smooth.
Add the eggs, mashed bananas, milk and vanilla, and mix well.
In a separate medium bowl, combine the flour, cocoa, baking soda, salt and cinnamon with a whisk.
Add the flour mixture to the banana mixture slowly, stirring until just combined.
Pour the batter into a greased 9x5 loaf pan.
Bake at 350 for 60-70 minutes, or until a toothpick inserted in the center comes out clean.
Allow the bread to cool for 10 minutes before transferring to a wire rack.