01 - Preheat oven to 350°F. Grease and flour a 9x5-inch loaf pan or line it with parchment paper.
02 - Whisk together flour, cocoa powder, baking soda, and salt in a medium bowl.
03 - In a large bowl, mash bananas. Add melted butter, sugar, eggs, and vanilla extract, then whisk until smooth.
04 - Gently fold the dry mixture into the wet ingredients until just combined without overmixing.
05 - Fold in chocolate chips and walnuts, if desired.
06 - Pour batter into the prepared loaf pan and smooth the surface evenly.
07 - Bake for 50 to 60 minutes until a toothpick inserted in the center comes out with moist crumbs.
08 - Allow the bread to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.