01 - Set oven to 425°F. Line two baking sheets with parchment paper and set aside.
02 - Peel onions and slice into 1/2-inch thick rings. Separate rings carefully.
03 - Combine flour, baking powder, smoked paprika, garlic powder, salt, and black pepper in a shallow bowl.
04 - Whisk eggs and buttermilk together in a separate bowl.
05 - Place panko breadcrumbs in a third shallow bowl.
06 - Dredge each onion ring first in the flour mixture, then dip in the egg mixture, and finally coat with panko breadcrumbs, pressing lightly to adhere.
07 - Place coated rings in a single layer on the prepared baking sheets and lightly spray with olive oil.
08 - Bake for 18 to 20 minutes, flipping halfway through, until golden and crispy.
09 - Whisk mayonnaise, sour cream, buttermilk, chives, dill, parsley, garlic powder, onion powder, salt, black pepper, and lemon juice until smooth. Chill until serving.
10 - Serve hot baked onion rings alongside chilled ranch dressing.