In a shallow bowl, whisk egg and buttermilk together until well combined.
In a second shallow bowl, whisk together flour, cornstarch, baking powder, bread crumbs, salt, garlic powder, onion powder, paprika, and black pepper until well combined.
In a third bowl, add oil.
Preheat air fryer to 400 degrees.
Working with one onion piece at a time, dip the entire onion piece in the egg/buttermilk mixture. Shake off excess liquid.
Next, place onion piece in breadcrumb mixture and cover entire ring with breading. Gently shake off excess breading.
You may place onions on a plate after you bread them.
Once you are ready to air fry the onions, dip each onion piece in the oil so that it is entirely covered in oil. Then, place onion in air fryer basket. NOTE: You do NOT need spray the air fryer basket.
Bake for 6-8 minutes, or until onions are golden brown. You will not likely need to flip them during the cooking time. NOTE: Time to bake will vary by brand of air fryer.