01 - Peel and slice onions into thick 1/2-inch rings. Separate into individual rings and set aside.
02 - Place flour in one bowl. Beat eggs in a second bowl. In a third bowl, combine panko breadcrumbs, smoked paprika, garlic powder, salt, and pepper.
03 - Heat olive oil in a skillet over medium heat. Add ground beef, salt, pepper, and Worcestershire sauce. Cook until browned, about 5–7 minutes. Remove from heat and let cool slightly.
04 - Stir pickles, tomatoes, shredded cheddar, ketchup, and mustard into the cooled beef mixture until well combined.
05 - Take the largest intact onion rings and fill each with the cheeseburger mixture, pressing gently to form a compact filling within the ring.
06 - Dredge each filled ring in flour, dip in beaten eggs, then coat thoroughly with the seasoned panko mixture.
07 - Heat vegetable oil in a deep fryer or large pot to 350°F. Fry the stuffed onion rings in batches for 2–3 minutes per side, or until golden brown and crispy. Drain on paper towels.
08 - Serve hot with your favorite burger sauce or dipping sauce.