01 - Preheat the oven to 350°F. Lightly grease a 9x5-inch loaf pan or line with parchment paper.
02 - In a large mixing bowl, thoroughly whisk together mashed bananas, eggs, vegetable oil, brown sugar, milk, and vanilla extract until fully blended.
03 - In a separate bowl, sift together all-purpose flour, unsweetened cocoa powder, ground cinnamon, baking soda, baking powder, and salt.
04 - Gradually fold the dry mixture into the wet ingredients just until incorporated. Avoid overmixing to maintain tenderness.
05 - Gently fold in chocolate chips or chopped walnuts, if desired.
06 - Transfer batter to the prepared loaf pan and smooth the surface evenly.
07 - Bake for 50 to 60 minutes or until a toothpick inserted in the center emerges clean or with only a few moist crumbs attached.
08 - Let cool in the pan for 10 minutes, then remove from the pan and transfer to a wire rack. Allow to cool completely before slicing.