01 - Preheat the oven to 350°F. Line a 12-cup muffin pan with paper liners or grease with nonstick spray.
02 - In a medium bowl, whisk together all-purpose flour, baking soda, salt, and cinnamon if using.
03 - In a large bowl, mash bananas then blend in melted butter, sugar, eggs, and vanilla extract until smooth.
04 - Fold dry ingredients gently into the wet mixture until just combined, avoiding overmixing.
05 - Fold in semisweet chocolate chips and chopped walnuts evenly.
06 - Spoon the batter evenly into prepared 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 moist crumbs.
08 - Allow muffins to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.