Slice the onions into 1/2-inch thick rings and separate them carefully.
In a large mixing bowl, combine the flour, garlic powder, paprika, salt, and black pepper.
In a separate bowl, pour in the buttermilk.
Dip each onion ring into the flour mixture, then into the buttermilk, and back into the flour mixture to coat thoroughly.
Once coated in flour, stuff each onion ring with shredded cheese, then dip it again in the buttermilk and coat in breadcrumbs.
Heat vegetable oil in a deep frying pan or large pot over medium heat. The oil should be about 2 inches deep.
Once the oil is hot (approximately 350°F/175°C), carefully add the prepared onion rings in small batches, ensuring not to overcrowd the pan.
Fry the onion rings for 3-4 minutes on each side until they are golden brown and crispy.
Use a slotted spoon to remove the rings from the oil and place them on a plate lined with paper towels to drain excess oil.
Serve hot with your favorite dipping sauce.