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 bananas until smooth. Add melted butter or oil, eggs, and vanilla extract. Whisk until completely combined.
04 - Pour wet mixture into dry ingredients. Fold gently with a spatula until just combined—batter should remain slightly lumpy. Do not overmix.
05 - Fold in chocolate chips and chopped nuts if using. Ensure even distribution throughout batter.
06 - Divide batter evenly among 12 muffin cups, filling each about three-quarters full.
07 - Bake for 18 to 22 minutes until golden brown and a toothpick inserted into center comes out clean.
08 - Let muffins cool in pan for 5 minutes. Transfer to wire rack and cool completely before serving.