In a large bowl, combine melted butter, brown sugar, and granulated sugar using a mixer or a hand whisk until well incorporated. Add eggs, vanilla extract, and mashed bananas. Whisk together until well combined.

Add dry ingredients to wet ingredients and mix until incorporated with a spatula. Set aside.

In a medium bowl, mix the melted chocolate and cocoa powder until well combined. Add 1/3 of the batter into the chocolate mixture and mix until well combined.

Drop dollops of plain batter and chocolate batter randomly into the pans with an ice cream scoop. Using a butter knife, swirl the batter to create the marble effect. Do not over swirl.

Bake for 25-30 minutes until a toothpick inserted into the bread comes out clean. Let cool in the pans for 10 minutes. Turn the little loaves out onto the wire rack to finish cooling.