Preheat your oven to 350°F (175°C). Grease and flour the loaf pan or line it with parchment paper.
In a mixing bowl, mash the ripe bananas with a fork until smooth. You should have about 1 ½ cups mashed banana.
Stir in the melted butter until well combined.
Add the granulated sugar and brown sugar, and mix until the sugars are dissolved.
Beat in the egg and vanilla extract until everything is combined.
Sprinkle the baking soda and salt over the mixture, and mix well.
Gradually add in the all-purpose flour and cocoa powder, folding gently until just combined (do not over-mix).
If using, fold in the chocolate chips for an extra chocolaty touch.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake in the preheated oven for about 60 minutes or until a toothpick inserted in the center comes out clean.
Once baked, remove the bread from the oven and let it cool in the pan for about 10 minutes. Then, transfer it to a cooling rack to cool completely.