Preheat oven to 375F. Line 12 muffin cups with parchment liners and set aside.
In a medium mixing bowl, whisk the flour, baking powder, baking soda, and salt; set aside.
In another mixing bowl, mash the bananas, whisk in the egg, greek yogurt, melted butter, brown sugar, and vanilla until combined. Add the flour mixture to the wet ingredients and whisk just until combined.
Divide batter evenly into 12 muffin cups. Top each muffin with 1 teaspoon of the cinnamon-sugar mixture and swirl with a toothpick or fork.
Bake for 20 minutes or until you can insert a toothpick and it comes out clean.