01 - Preheat oven to 350°F. Line a 9 x 5 inch loaf pan with parchment paper or grease lightly with butter or cooking spray.
02 - In a large mixing bowl, whisk together mashed bananas, eggs, vegetable oil, brown sugar, and vanilla extract until smooth and well combined.
03 - In a separate bowl, sift together all-purpose flour, unsweetened cocoa powder, baking soda, and salt to eliminate lumps and evenly distribute leavening agents.
04 - Gradually fold dry ingredients into wet mixture using a spatula until just combined. Do not overmix as this develops gluten and results in dense bread.
05 - Gently fold in dark chocolate chips and walnuts if desired, distributing evenly throughout batter.
06 - Pour batter into prepared loaf pan and smooth the top surface with a spatula for even baking.
07 - Bake for 50 to 55 minutes until a toothpick inserted into the center emerges with a few moist crumbs attached.
08 - Allow bread to cool in pan for 10 minutes, then turn out onto a wire rack to cool completely before slicing.