Preheat the oven to 350°F (175°C) and line a loaf pan with parchment paper.
Mash the bananas in a bowl until smooth.
Add espresso, melted coconut oil, brown sugar, and vanilla extract, mixing well.
In another bowl, whisk together flour, cocoa powder, baking soda, and salt.
Gradually combine the dry ingredients with the wet mixture, stirring until just blended.
Fold in the chopped hazelnuts for a crunchy texture.
Pour batter into the loaf pan and spread evenly.
Bake for 50 minutes or until a toothpick inserted comes out clean.
Let cool for 10 minutes before slicing.