Move the oven rack to the middle position and preheat to 350 degrees F (175 C). Use a paper towel to evenly spread some vegetable oil or butter along the bottom and sides of a 9" loaf pan, and then dust with flour. Flip the pan over over the sink and tap out any excess flour.
In a large glass bowl, microwave the bananas, butter, sugar and salt for 3 minutes. Watch it closely and stop it for a few seconds if it looks like it's going to boil over. Let this mixture cool until it's luke warm.
In a medium bowl, sift together the all-purpose flour, coco powder and baking soda to remove any clumps. Add the chocolate chips and then whisk the mixture together.
When the bananas have cooled, put them in a blender or food processor along with the eggs, yogurt, and vanilla extra. Blend until smooth.
Pour the banana mixture into the flour mixture and fold together with a spatula until it's just combined, it's okay if there are still some steaks of flour remaining, but do not over mix.
Pour the batter into the prepared loaf pan and place it in the oven. Bake for 40-50 minutes, or until a toothpick inserted into the center comes out clean.
Cool the banana bread on a wire rack for 15 minutes, then remove the loaf from the pan and let it cool completely.