01 - Heat the oven to 425°F. Line two baking sheets with parchment paper and lightly coat with cooking spray.
02 - Peel the onions and cut into ½-inch thick rings. Separate individual rings and discard the smallest inner pieces.
03 - Set up three shallow bowls: bowl one with flour, salt, black pepper, garlic powder, onion powder, and smoked paprika whisked together; bowl two with beaten eggs and buttermilk combined; bowl three with panko breadcrumbs mixed with grated Parmesan cheese.
04 - Dip each onion ring into the seasoned flour mixture, ensuring a thorough coating, then shake off excess.
05 - Submerge floured rings into the egg and buttermilk mixture, allowing excess liquid to drip off.
06 - Dredge the rings in the panko-Parmesan blend, pressing gently to adhere the coating evenly.
07 - Place coated rings in a single layer on the prepared baking sheets and lightly spray their tops with cooking spray.
08 - Bake for 10 minutes, flip each ring, then bake an additional 8–10 minutes until golden and crisp.
09 - Remove from oven and serve immediately while hot.