01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or lightly grease it.
02 - In a large bowl, mash the bananas then whisk in eggs, vegetable oil, yogurt or sour cream, and vanilla extract until fully blended.
03 - In another bowl, whisk together flour, granulated sugar, brown sugar, baking soda, baking powder, salt, and cinnamon if using.
04 - Add dry ingredients to wet ingredients and gently stir just until combined; avoid overmixing.
05 - Fold in the semi-sweet chocolate chips and chopped walnuts evenly into the batter.
06 - Divide batter evenly among muffin cups, filling each about three quarters full.
07 - Bake for 18 to 22 minutes or until a toothpick inserted in the center comes out clean or with a few moist crumbs.
08 - Allow muffins to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.