Preheat oven to 325 F. Butter and flour 9x 5-inch loaf pan.
Note: To help preserve any banana chunks in mashed bananas, it is best to mix by hand. However, if keeping the chunky bananas isn't important, use a stand mixer, but mix only until just combined. Avoid over mixing the batter.
In a medium bowl, whisk together butter and eggs. Stir in mashed bananas, vanilla and salt. In a large bowl mix together flour, cocoa powder, sugar, baking powder, and baking soda. Whisk wet ingredients into dry ingredients, mixing until combined. Stir in nuts and chocolate chips.
Pour batter into prepared loaf pan. Bake in preheated oven on center rack for 50 to 60 minutes or until a knife inserted in the center comes out clean. Place loaf pans on a wire rack to cool.