Preheat the oven to 375°F (190°C). Grease a 5 x 9–inch (13 x 23–cm) loaf pan with olive oil, avocado oil or coconut oil spray.
In a large mixing bowl, mix together the mashed bananas, almond milk, maple syrup, vegan butter, vanilla, cinnamon, baking powder and baking soda. Then, add the quick oats and flour and mix until smooth. Spoon half of the batter into the greased loaf pan.
Add the cocoa powder to the remaining batter and mix until smooth. Use a tablespoon to spoon the cocoa banana bread batter down the top-center of the regular banana bread batter.
Top the batter with banana slices and bake for 40 to 50 minutes, or until golden brown and a toothpick inserted in the center of the bread comes out clean.
Store any leftover banana bread at room temperature wrapped in plastic or sealed tightly with aluminum foil.