In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda, salt and sugar.
In a small bowl, mash banana. Mix in buttermilk, egg, vanilla and vegetable oil until well combined.
Pour the wet ingredients into dry ingredients and mix until just combined. The mixture should still be pretty lumpy.
Spray a large pan with nonstick cooking spray and set to medium heat. Cook pancakes until bubbles form on the surface and edges are just cooked, about 2 minutes. Flip and cook for an additional minute.
Garnish with additional banana slices and drizzle with maple syrup or honey, if desired.