Preheat oven to 350°F (175°C) and line a loaf pan with parchment paper.
Mash bananas in a large bowl until smooth.
Stir in melted butter, brown sugar, eggs, and vanilla extract.
In a small bowl, dissolve espresso powder in hot water.
Add espresso mixture to the banana mixture and stir well.
In a separate bowl, whisk together flour, baking soda, and salt.
Gradually combine dry ingredients with the wet mixture.
Fold in the chopped nuts.
Pour the batter into the prepared loaf pan.
Bake for 50-55 minutes or until a toothpick comes out clean.
Let cool before slicing.