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 smallest inner rings for other uses.
03 - Set up three shallow bowls: mix flour, garlic powder, smoked paprika, salt, and pepper in the first; whisk eggs and milk in the second; place panko breadcrumbs in the third.
04 - Dip each onion ring in flour mixture, then egg mixture, and finally coat thoroughly with panko breadcrumbs. Arrange coated rings on prepared baking sheets.
05 - Lightly spray onion rings with cooking spray or drizzle with olive oil to enhance crispiness.
06 - Bake for 20 to 25 minutes, flipping halfway through, until golden brown and crisp.
07 - Combine mayonnaise, sour cream, buttermilk, chives, parsley, dill, garlic powder, onion powder, salt, pepper, and lemon juice in a bowl. Mix until smooth and refrigerate until serving.
08 - Serve hot, crispy onion rings alongside ranch dressing.