Preheat oven to 350° F. Spray a 9x5-inch loaf pan with cooking spray. Line the bottom and two long sides of the loaf pan with a piece of parchment paper, leaving a little overhang on the two long edges. This makes it easier to remove the bread from the pan.
In a medium mixing bowl, whisk together the flour, cocoa powder, baking soda and salt.
1 ¼ cups all-purpose flour, ½ cup unsweetened cocoa powder, 1 teaspoon baking soda, ½ teaspoon salt
In a large mixing bowl, combine the melted butter, mashed banana, brown sugar, granulated sugar, eggs and vanilla. Whisk until well combined.
½ cup unsalted butter, 1 ½ cups mashed ripe banana, ½ cup packed light brown sugar, ¼ cup granulated sugar, 2 large eggs, 1 teaspoon vanilla extract
Pour the dry ingredients into the wet. Mix with a rubber spatula until just combined, being careful to not overmix. Gently mix in the chocolate chips.
¾ cup chocolate chips
Pour the batter into the prepared baking pan. Sprinkle a few more chocolate chips on top of the loaf, and gently press them into the batter slightly (just a bit).
Bake for 55-65 minutes, loosely covering/tenting the top of the loaf with foil after about 35-40 minutes to prevent it from over-browning. The bread is done when a toothpick inserted into the center of the loaf comes out clean, except for possibly melted chocolate chips or a few moist crumbs.
Let bread cool in the pan for 15 minutes and then use the parchment paper overhang to remove it to a wire rack to finish cooling. It's best to let the bread cool for at least 30 minutes before slicing; if you slice it when it's hot it may crumble.