Spray a 9x5-inch loaf pan with cooking spray and line with parchment paper. Make sure there is an overhang on the sides of the pan for easy removal.
Preheat oven to 350°F.
In a small bowl combine the flour, cacao powder, cinnamon, soda and salt. Whisk.
In a small bowl mash 3 of the bananas until mostly broken down but still some small chunks still remain. Slice the remaining 1 banana in half lengthwise.
In a stand mixer fitted with a paddle attachment combine the grapeseed oil with both sugars. Beat on low for 3-5 minutes or until the sugars have melted into the oil. Next, add in the eggs one at a time and mix until fully incorporated. Add in the 3 mashed bananas and vanilla and mix for 1 minute more.
Lastly, slowly add the dry ingredients into the wet and mix until you no longer see any flour. Be sure not to overwork the batter.
Pour into the prepared loaf pan and top with the sliced banana, cut side up. Bake for 60-65 minutes or until a toothpick inserted in the middle comes out clean. Cool for 10 minutes then remove from the pan and let cool fully on a baking rack.
Recipe Courtesy of Megan Mitchell