Add sugar and cinnamon to a place and mix together. Set aside. Add the egg and ½ tsp cinnamon to a bowl and beat together. Cut off the crust of each slice of bread and roll until very flat. Spread 1 tbsp of Nutella on each slice, top with banana slices, and roll up. Dip each roll in the egg, turning all the way around, and shake off excess.

Melt the butter in a skillet and fry each french toast roll-up by turning with tongs until browned all the way around, about 5 minutes each. Immediately roll the roll-up in the sugar cinnamon mixture and set aside on a plate. Keep warm in an oven (200 degrees F) if desired until ready to serve. Sprinkle with powdered sugar before serving.