Preheat oven to 350°F (175°C) and grease a loaf pan.
In a large bowl, mash bananas until smooth.
Stir in melted butter, brown sugar, eggs, and vanilla until combined.
In a separate bowl, whisk together flour, baking soda, salt, and cinnamon.
Gradually add dry ingredients to the wet mixture, stirring until just combined.
For the mocha filling, heat heavy cream in a small saucepan until warm.
Remove from heat and stir in chocolate chips, espresso powder, cocoa powder, and vanilla.
Mix until smooth and glossy.
Pour half of the banana batter into the loaf pan.
Spread the mocha filling evenly over the batter.
Top with the remaining banana mixture and swirl slightly for a marbled effect.
Bake for 50-55 minutes, or until a toothpick inserted in the center comes out clean.
Let cool for at least 15 minutes before slicing.