01 - Separate onion slices into individual rings. In a bowl, combine flour, smoked paprika, garlic powder, and salt. Whisk eggs in a separate bowl. Place panko breadcrumbs in a third bowl. Dredge each onion ring in flour mixture, dip into beaten eggs, then coat thoroughly with breadcrumbs.
02 - Heat vegetable oil in a deep skillet over medium-high heat. Fry breaded onion rings in batches until golden brown and crispy, approximately 2-3 minutes per batch. Transfer to paper towels to drain excess oil.
03 - Heat a non-stick skillet over medium heat. Place one tortilla in the pan and sprinkle with one-quarter of the cheddar and mozzarella cheeses. Arrange several fried onion rings evenly over the cheese. Drizzle with 2 tablespoons sour cream and add chives if desired. Top with a second tortilla.
04 - Cook for 2-3 minutes until the bottom tortilla is golden brown. Carefully flip and cook for an additional 2 minutes until the second side is golden and cheese is completely melted. Repeat with remaining ingredients.
05 - Let quesadillas rest for 1-2 minutes, then cut into wedges. Serve immediately with salsa, guacamole, and additional sour cream on the side.