01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or lightly grease it.
02 - In a large bowl, whisk mashed bananas, eggs, vegetable oil, brown sugar, and vanilla extract until smooth.
03 - In a separate bowl, stir together all-purpose flour, baking powder, baking soda, salt, and ground cinnamon if using.
04 - Add the dry ingredients to the wet mixture and gently fold until just combined, taking care not to overmix.
05 - Fold in the semi-sweet chocolate chips and chopped nuts if desired.
06 - Distribute batter evenly among muffin cups, filling each about three-quarters full.
07 - Sprinkle additional chocolate chips atop each muffin if preferred.
08 - Bake for 18 to 22 minutes until a toothpick inserted into the center emerges clean or with a few moist crumbs.
09 - Allow muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.