01 - Combine buttermilk, garlic powder, onion powder, salt, and black pepper in a bowl. Submerge chicken fillets, cover, and refrigerate for at least 15 minutes or up to 4 hours.
02 - Mix flour, panko breadcrumbs, and grated Parmesan in a shallow dish. In a separate bowl, beat eggs until smooth.
03 - Remove chicken from marinade. Dredge each fillet in flour mixture, dip into beaten egg, then coat again in flour mixture for a double-crisp crust.
04 - Pour vegetable oil to a depth of 1/2 inch in a large skillet and heat to 350°F. Fry chicken fillets for 3-4 minutes per side until golden and fully cooked. Drain on paper towels.
05 - In a mixing bowl, coat romaine lettuce with Caesar dressing. Add shaved Parmesan, gently tossing to combine.
06 - If desired, spread butter on split buns and toast in a skillet until golden and crisp.
07 - Place a fried chicken fillet on the bottom half of each bun. Top with Caesar salad. Cap with the remaining bun halves and serve immediately.