In a small skillet, melt the butter over medium heat and cook the onion and cook for about 4-5 minutes.
Remove from the heat and set aside to cool slightly.
Meanwhile, in a bowl, add the eggs, soy sauce and black pepper and beat well.
Add the cooked onion and gently stir to combine.
Place the onion mixture into a small baking pan.
Slide the Air Fryer Basket inside and adjust the temperature to 350 °F to preheat for 5 minutes.
After preheating, arrange the baking pan into the Air Fryer Basket.
Slide the basket into Air Fryer and set the time for 5 minutes.
After cooking time is finished, remove the baking pan from Air Fryer and set aside for about 5 minutes.
Cut into equal-sized wedges and serve.