Cut the ends off of the onion to remove the skin. Slice into thick rings, about 1/4-1/2 inch in thickness. Carefully separate each ring.
Toss in buttermilk and cover, either in a bowl or in a gallon sized Ziploc bag, refrigerated for 30-60 minutes.
Shake off and discard excess buttermilk.
Use three large bowls for the dredging process. One bowl for the flour, one for two eggs lightly whisked, one for panko breadcrumbs and seasoning.
Dredge in flour, then in whisked eggs, lastly in the panko mixture.
Lay in an air fryer basket in batches, careful not to overcrowd the basket. Spray with oil, being sure to cover any bare flour spots as best as you can.
Air fry at 325F for 10 minutes.
This recipe can be easily be doubled. However, I recommend a new batch of dredges for each onion in clean bowls. Otherwise everything gets too sticky and doesn’t coat well. Do one onion at a time. You can soak multiple onions in one Ziploc of buttermilk.