Separate onion slices into rings.
In a shallow dish, mix together the flour, baking powder, and salt.
In a second dish, add milk and egg and beat slightly.
In a third dish, place the breadcrumbs.
Coat each onion ring with flour mixture, then dip into egg mixture and finally, coat with the breadcrumbs.
Grease the Air Fryer Basket with cooking spray and then slide inside.
Adjust the temperature of Air Fryer to 360 °F to preheat for 5 minutes.
After preheating, arrange the onion rings into the greased Air Fryer Basket in a single layer.
Slide the basket into Air Fryer and set the time for 8-10 minutes.
After cooking time is finished, remove the onion rings from Air Fryer and serve.