Cut the pastry sheet into 4 equal-sized squares.
Spread Nutella on each square of pastry evenly.
Divide the banana slices over Nutella.
Fold each square into a triangle and with wet fingers, slightly press the edges.
Then with a fork, press the edges firmly.
Grease the Air Fryer Basket with cooking spray and then slide inside.
Adjust the temperature of Air Fryer to 375 °F to preheat for 5 minutes.
After preheating, arrange the pastries into the greased Air Fryer Basket in a single layer.
Slide the basket into Air Fryer and set the time for 10-12 minutes.
After cooking time is finished, remove the pastries from Air Fryer and serve warm.