01 - Preheat oven to 425°F. Line two baking sheets with parchment paper and lightly grease with cooking spray or olive oil.
02 - Separate onion slices into rings, reserving the smallest inner rings for another use.
03 - Arrange three shallow bowls: one with flour, garlic powder, smoked paprika, salt, and pepper; one with whisked eggs and milk; one with panko breadcrumbs.
04 - Dip each onion ring into the flour mixture, then egg mixture, and finish by coating thoroughly with panko breadcrumbs. Place on prepared baking sheets.
05 - Lightly spray coated onion rings with cooking spray or drizzle with olive oil for enhanced crispiness.
06 - Bake for 20 to 25 minutes, flipping halfway through, until golden brown and crispy.
07 - Combine mayonnaise, sour cream, buttermilk (or milk), chives, parsley, dill, garlic powder, onion powder, salt, black pepper, and lemon juice in a bowl. Whisk until smooth and refrigerate until serving.
08 - Serve the hot, crispy onion rings with ranch dressing on the side.