01 - Preheat oven to 350°F. Grease and line a 9x5-inch loaf pan with parchment paper.
02 - Whisk together flour, cocoa powder, baking soda, and salt in a medium bowl until well blended.
03 - Combine mashed bananas, sugar, oil, peanut butter, eggs, and vanilla in a large bowl. Beat until smooth and creamy.
04 - Add dry ingredients to wet mixture. Stir gently until just combined, being careful not to overmix.
05 - Fold chocolate chips into batter until evenly distributed.
06 - Transfer batter to prepared loaf pan. Dollop extra peanut butter on surface and swirl gently with a knife.
07 - Bake for 50-55 minutes until a toothpick inserted into center comes out with just a few moist crumbs.
08 - Cool in pan for 10 minutes, then remove to wire rack to cool completely before slicing.