01 - Preheat the oven to 350°F. Grease and line a 9x5-inch loaf pan with parchment paper.
02 - In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt until well blended.
03 - In a large bowl, combine mashed bananas, sugar, oil, peanut butter, eggs, and vanilla. Mix until smooth and creamy.
04 - Add the dry ingredients to the wet ingredients. Stir gently until just combined; do not overmix to maintain tender texture.
05 - Fold in the chocolate chips until evenly distributed throughout the batter.
06 - Pour the batter into the prepared loaf pan. Dollop extra peanut butter on top and swirl gently with a knife to create marbled pattern.
07 - Bake for 50–55 minutes, or until a toothpick inserted into the center comes out with just a few moist crumbs.
08 - Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.