Preheat the oven to 350°F (175°C) and grease a loaf pan.
Mash the bananas in a large bowl until smooth.
Stir in melted butter, brown sugar, eggs, and vanilla extract.
In another bowl, whisk together flour, baking soda, salt, and cinnamon.
Gradually add the dry mixture to the wet ingredients, stirring until just combined.
Fold in the chopped walnuts for that perfect crunch.
For the mocha filling, heat the 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.
Add the remaining banana mixture and gently swirl with a knife.
Bake for 50-55 minutes or until a toothpick inserted in the center comes out clean.
Let it cool for at least 15 minutes before slicing (or just accept the inevitable burns).