01 - Separate onion slices into individual rings. Set up three shallow bowls: mix flour, smoked paprika, garlic powder, and salt in the first; whisk eggs in the second; place panko breadcrumbs in the third.
02 - Dredge each onion ring in the flour mixture, shaking off excess. Dip into beaten eggs, allowing excess to drip off. Press firmly into panko breadcrumbs to coat evenly on all sides.
03 - Heat 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 paper towels to drain excess oil.
04 - Heat a non-stick skillet over medium heat. Place one flour tortilla in the pan. Sprinkle evenly with 1/2 cup cheddar cheese and 1/4 cup mozzarella cheese.
05 - Arrange fried onion rings over the cheese layer. Drizzle with 2 tablespoons sour cream and sprinkle with chives if desired. Top with second tortilla.
06 - Cook for 2-3 minutes until bottom tortilla is golden brown and cheese begins to melt. Carefully flip using a spatula and cook another 2 minutes until second side is golden and cheese is fully melted.
07 - Transfer quesadilla to a cutting board. Let cool for 1 minute, then cut into 4-6 wedges. Serve immediately with salsa, guacamole, and additional sour cream on the side.