Preheat oven to 425°F degrees. Line a 12-count muffin pan with muffin liners or spray with nonstick spray. Set aside.
In a medium bowl, mix the mashed bananas, maple syrup, yogurt, egg, milk, butter and vanilla together until smooth..
In a large bowl, whisk together the flour, cocoa, baking soda, baking powder, salt. Pour the dry ingredients into the wet ingredients and stir until just combined. Fold in 1/2 cup of chocolate chips. Do not overmix the batter or you will have tough muffins.
Evenly distribute the batter between the muffin cups. (I use an ice cream scoop for easy portioning). Sprinkle remaining 1/4 cup of chocolate chips evenly on the tops. Bake for 5 minutes at 425°F degrees. Keeping the muffins in the oven, reduce the oven temperature to 350°F and continue to bake for another 17 minutes or until a toothpick inserted in the center comes out clean.