01 - Preheat oven to 425°F. Line two baking sheets with parchment paper and lightly spray with cooking spray.
02 - Peel onions and slice into ½-inch thick rings. Separate into individual rings, discarding the very small inner ones.
03 - Set up three shallow bowls: Bowl 1 with flour, salt, pepper, garlic powder, onion powder, smoked paprika whisked together. Bowl 2 with beaten eggs and buttermilk combined. Bowl 3 with panko breadcrumbs mixed with grated Parmesan.
04 - Dip each onion ring into flour mixture, shaking off excess. Submerge into egg-buttermilk mixture, letting excess drip off. Dredge in panko-Parmesan mixture, pressing gently to adhere.
05 - Place coated rings on baking sheets in a single layer and lightly spray tops with cooking spray.
06 - Bake for 10 minutes until edges start browning.
07 - Flip each ring and bake an additional 8 to 10 minutes until golden and crispy.
08 - Remove from oven and serve immediately while hot.