Peel and slice the onions into ½-inch thick rings. Separate the rings and set aside.
- Prepare the breading station: In one shallow bowl, combine the flour, garlic powder, paprika, salt, and pepper. In a second bowl, whisk the egg. In a third bowl, place the breadcrumbs and Parmesan cheese (if using).
- Dip each onion ring into the flour mixture, then into the egg wash, and finally coat with the breadcrumb mixture, pressing gently to ensure the breadcrumbs stick.
- Preheat the air fryer to 375°F (190°C) for 5 minutes.
- Lightly spray the air fryer basket with cooking spray. Arrange the onion rings in a single layer in the basket (working in batches if necessary).
- Air fry the onion rings for 8-10 minutes, flipping halfway through, until golden brown and crispy.
- Serve immediately with your favorite dipping sauce.