Adjust oven rack to lower-middle position and preheat oven to 425. Spray a muffin tin with non-stick spray or line with cupcakes liners and set aside. Mix flour, baking powder, baking soda, salt and nutmeg in a medium bowl.
In the bowl of a stand mixer, beat sugar and butter on medium speed until light and fluffy. Add eggs, one at a time, beating until combined. Reduce speed to low and add dry ingredients in two installments, alternating with 3 additions of yogurt. Gently fold in chopped bananas and peanut butter chips by hand. DO NOT OVER MIX, or your muffins will turn out hard and tough.
Divide batter evenly among muffin cups. Don't be afraid to fill them all the way to the top!
Bake for 5 minutes at 425, and then lower oven temperature to 375. Bake another 15 to 18 minutes, or until muffins are golden brown and a toothpick inserted in the center comes out clean.
Remove muffins from tin to wire rack and allow to cool for 5 minutes. Meanwhile, combine turbinado sugar and cinnamon in a small bowl. Dip cooled muffins in melted butter and then roll in cinnamon-sugar mixture.