Begin by heating vegetable oil in a deep fryer or a large pot to 350°F (175°C). Ensure there is enough oil to submerge the onion rings completely.
In a medium bowl, combine the flour, garlic powder, paprika, salt, and black pepper. Mix well.
In another bowl, pour the buttermilk.
Dip each onion ring first into the buttermilk, allowing any excess to drip off, then coat it in the flour mixture, shaking off any excess.
Return the coated onion ring to the buttermilk, then dredge it in the panko breadcrumbs, pressing gently to ensure the crumbs adhere well.
Carefully place the coated onion rings into the hot oil, frying in batches to avoid overcrowding. Fry for about 2-3 minutes or until golden brown and crispy.
Remove the onion rings with a slotted spoon and place them on a paper towel-lined plate to drain excess oil.
Serve warm with your favorite dipping sauce.