Preheat oven to 350°F (175°C) and line a loaf pan with parchment paper.
In a bowl, mash bananas until smooth.
Mix in melted butter, brown sugar, eggs, and vanilla extract.
In another bowl, whisk together flour, baking soda, salt, and cinnamon.
Slowly combine dry ingredients with the banana mixture.
In a small bowl, dissolve espresso powder in hot water, then mix with brown sugar.
Pour half of the batter into the loaf pan.
Drizzle half of the coffee mixture over the batter.
Add the remaining batter, then swirl in the rest of the coffee mixture using a spoon.
Bake for 50-55 minutes or until a toothpick comes out clean.
Let cool before slicing.