Preheat the oven to 350°F (175°C) and grease a loaf pan.
Mash bananas in a bowl until smooth.
Stir in melted butter, brown sugar, eggs, and vanilla.
Whisk together flour, baking soda, salt, and cinnamon in a separate bowl.
Fold dry ingredients into the banana mixture until just combined.
For the mocha swirl, heat heavy cream in a saucepan until warm.
Remove from heat and stir in chocolate chips, espresso powder, cocoa, and vanilla.
Take ⅓ cup of the banana batter and mix it with the mocha swirl.
Pour the regular batter into the loaf pan.
Dollop the mocha mixture on top and swirl with a toothpick.
Bake for 50-55 minutes until a toothpick inserted in the center comes out clean.
Cool for 15 minutes before slicing—if you can wait that long.