01 - Preheat oven to 425°F. Line two baking sheets with parchment paper and lightly coat with cooking spray.
02 - Peel onions and cut into ½-inch thick rings. Separate individual rings, discarding the very small inner rings.
03 - In three shallow bowls, combine ingredients as follows: Bowl 1 - flour, salt, black pepper, garlic powder, onion powder, and smoked paprika whisked together; Bowl 2 - beaten eggs and buttermilk combined; Bowl 3 - panko breadcrumbs mixed with grated Parmesan.
04 - Dip each onion ring into the flour mixture, shaking off excess; then submerge into egg-buttermilk mixture, allowing excess to drip off; finally dredge in panko-Parmesan mixture, pressing gently to ensure adhesion.
05 - Place coated onion rings in a single layer on the prepared baking sheets and lightly spray the tops with cooking spray.
06 - Bake for 10 minutes, flip each ring, then bake an additional 8–10 minutes until golden and crisp.
07 - Remove from oven and serve immediately while hot.