Heat a nonstick skillet over medium heat. Working one at a time, lightly brush melted butter on both sides of the flatbread. Warm in skillet for 30 seconds per side. Remove and set aside.
Working quickly, spread a thin, even layer of peanut butter and marshmallow fluff across each flatbread. Top with banana slices and chocolate chips. Fold in half length-wise and then again width-wise. Sprinkle with powdered sugar and devour immediately.