01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with paper liners or grease it lightly.
02 - In a large bowl, mash the bananas. Whisk in the eggs, vegetable oil, yogurt or sour cream, and vanilla extract until the mixture is smooth.
03 - In a separate bowl, whisk together the all-purpose flour, granulated sugar, brown sugar, baking soda, baking powder, salt, and cinnamon if using.
04 - Add the dry ingredients to the wet ingredients and gently stir until just combined, avoiding overmixing.
05 - Fold in the semi-sweet chocolate chips and chopped walnuts evenly into the batter.
06 - Divide the batter evenly among the prepared muffin cups, filling each about 3/4 full.
07 - Bake for 18 to 22 minutes, or until a toothpick inserted into the center of a muffin comes out clean or with a few moist crumbs.
08 - Allow muffins to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.