01 - Separate onion slices into individual rings. Set up three shallow bowls: mix flour, smoked paprika, garlic powder, and salt in the first bowl, whisk eggs in the second bowl, and place panko breadcrumbs in the third bowl.
02 - Dredge each onion ring in the seasoned flour mixture, shaking off excess. Dip into the beaten eggs, then press into panko breadcrumbs to coat evenly. Repeat until all rings are breaded.
03 - Heat 2 inches of vegetable oil in a deep skillet over medium-high heat until it reaches 350°F. Fry onion rings in batches for 2-3 minutes until golden brown and crispy. Transfer to a paper towel-lined plate to drain excess oil.
04 - Heat a non-stick skillet over medium heat. Place one tortilla in the skillet and sprinkle with 1/2 cup cheddar cheese and 1/4 cup mozzarella cheese, distributing evenly.
05 - Arrange 4-5 crispy onion rings over the cheese layer. Drizzle with 2 tablespoons sour cream and sprinkle with 1/2 tablespoon fresh chives if using.
06 - Top with a second tortilla. Cook for 2-3 minutes until the bottom tortilla is golden brown. Carefully flip and cook for another 2 minutes until the cheese is completely melted and the second side is golden.
07 - Transfer quesadilla to a cutting board and let cool for 1 minute. Cut into 6 wedges. Serve immediately with salsa, guacamole, and additional sour cream on the side. Repeat with remaining ingredients to make 4 quesadillas total.