Preheat oven to 375°F. Line a 12-cup muffin tin with liners or grease lightly.
Whisk flour, baking powder, baking soda, salt, and cinnamon in a bowl.
Mash bananas in a large bowl. Whisk in granulated sugar, brown sugar, eggs, melted butter, yogurt, and vanilla until smooth.
Fold dry ingredients into the banana mixture just until no dry streaks remain.
Stir in walnuts gently. Do not overmix.
Divide batter among muffin cups, filling each about three-quarters full. Sprinkle tops with turbinado sugar if using.
Bake 16–19 minutes, until golden and a toothpick comes out with a few moist crumbs.
Cool 5 minutes in the pan, then transfer muffins to a rack to finish cooling.