01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or grease lightly with cooking spray.
02 - In a large mixing bowl, whisk together flour, oats, sugar, baking soda, baking powder, salt, and cinnamon until thoroughly blended.
03 - In a separate bowl, mash ripe bananas until smooth. Add melted butter or oil, eggs, and vanilla extract. Whisk until uniform consistency.
04 - Pour wet ingredients into dry ingredients. Fold gently with a spatula until just combined—small lumps should remain. Avoid overmixing to prevent tough muffins.
05 - Fold in semi-sweet chocolate chips and chopped nuts if using. Distribute evenly throughout batter.
06 - Divide batter equally among 12 muffin cups, filling each about three-quarters full.
07 - Bake for 18–22 minutes until golden brown and a toothpick inserted into the center comes out clean.
08 - Let muffins cool in pan for 5 minutes before transferring to wire rack. Cool completely before storing.