Preheat the oven to 350°F. Spray a 12-cup muffin pan with non-stick spray or line it with cupcake liners.
Mash the banana in a large bowl. Add 1 cup yogurt, ½ cup peanut butter, ½ cup applesauce, and an egg. Stir until well combined and smooth.
Place the flour and baking soda in a small bowl. Stir or whisk to combine.
Add the flour mixture to the wet mixture and stir to combine.
Spoon the batter into the cups evenly, filling about half full.
Bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool completely.
Place ½ cup Greek yogurt and ¼ cup peanut butter in a small bowl. Stir until combined. Spread the frosting on top of the cupcakes.
Store leftovers in an airtight container in the fridge.