In a medium bowl, add the egg and the milk. Whisk until frothy and well-combined. Add the sliced onions and soak them for 10 minutes.
In a separate bowl, mix together the all-purpose flour, garlic powder, breadcrumbs, and the sea salt and black pepper.
Take the sliced onions that have been soaking in the egg mixture, and dredge them through the flour mixture until lightly coated.
Place the coated onion slices in a single layer in the air fryer basket. Coat with cooking spray, and air fry at 380 degrees Fahrenheit for 14 minutes, shaking the onions halfway.
Add crispy fried onions to green bean casseroles, on burgers, or soups and salads. Or just enjoy plain in your favorite dipping sauce! Store leftovers in an airtight container for up to 2 days.