Preheat the oven to 375°F (190°C).
Line 16 regular-size muffin cups with paper liners and lightly spray with non-stick spray. (Note 2)
In a large bowl, mash thawed bananas with a fork or wooden spoon.
Add sugar, melted butter and vanilla extract, and mix everything until combined.
Then stir in lightly beaten egg.
Add flour, baking soda, baking powder and salt. Mix until just combined. Don't overman the batter.
Add walnuts and/or chocolate chips, if using.
Divide the batter evenly into the prepared muffin cups. (TIP: Use a large cookie scoop to evenly divide the batter. 1 scoop into each muffin cup.)
Bake for 18-20 minutes, or until the inserted toothpick comes out clean. Cool completely before serving.
