Preheat oven to 350°F (175°C). Line a muffin tin with paper liners or grease the cups.
- In a large bowl, combine oats, flour, baking powder, baking soda, cinnamon, and salt.
- In another bowl, whisk mashed bananas, brown sugar or maple syrup, yogurt or milk, egg, and vanilla extract.
- Add wet ingredients to dry ingredients and stir just until combined. Fold in nuts or chocolate chips if using.
- Spoon batter into muffin tin, filling each cup about 3/4 full.
- Bake for 18-22 minutes or until a toothpick inserted in the center comes out clean.
- Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.