In a large mixing bowl, use a fork to mash the bananas until they are smooth. Add the sugar, oil, egg and vanilla. Whisk vigorously for about one minute until combined.
In a separate medium bowl, whisk together the flour, baking soda and salt. Dump the flour mixture and the chocolate chips into the bowl with the wet ingredients. Use a rubber spatula to gently fold together the muffin batter just until no streaks of flour remain. Don't over mix or your muffins can become tough.
Use a 1/4-cup capacity measuring scoop to distribute the batter evenly into 12 muffin cups. Sprinkle 4-6 additional chocolate chips on top of each muffin. Bake in the preheated oven at 425 degrees F for 7 minutes. Do not open the oven door. Reduce the heat to 350 degrees F and bake for 3 more minutes.
Rotate the muffin pan front to back. Continue baking at 350 degrees F for 10-12 minutes, or until a toothpick inserted into the center comes out clean. Allow the muffins to cool in the pan for 5 minutes. Then carefully remove them to a cooling rack to allow them to finish cooling to room temperature.