First, prepare the breadcrumbs. Tear the two slices of bread into 1" pieces and add them to a baking sheet.
Bake the bread at 350 degrees F for 5-7 minutes, stirring halfway through. Keep an eye on the bread so it doesn't burn.
Once the bread has cooled, add it to a food processor. Pulse until it is a breadcrumb consistency. Pour the breadcrumbs into a bowl and stir in the garlic powder.
Add the egg to a separate bowl and whisk it.
Cut the ends off the onion and peel it. Cut into rings, about 1/4" thick.
Dip the onion rings (one at a time) in the egg wash, then the breadcrumbs. Then place in the air fryer. Do not overlap the onion rings, you may have to cook more than one batch.
Spray the onion rings with cooking spray. Cook in the air fryer for 7 minutes, turning halfway through and spraying again with cooking spray. Let cool and serve.