01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or grease lightly.
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 flour, baking powder, baking soda, salt, and cinnamon if using.
04 - Add dry ingredients to wet mixture and gently stir until just combined, avoiding overmixing.
05 - Fold in chocolate chips and nuts if desired, ensuring even distribution.
06 - Divide batter evenly into prepared muffin cups, filling each about three-quarters full.
07 - Sprinkle additional chocolate chips on top of each muffin if preferred.
08 - Bake for 18 to 22 minutes until a toothpick inserted in the center comes out clean or with few moist crumbs.
09 - Let the muffins cool in the pan for 5 minutes before transferring to a wire rack to cool completely.