01 - Whisk buttermilk with garlic powder, onion powder, salt, and black pepper in a bowl. Submerge chicken fillets, cover, and refrigerate for a minimum of 15 minutes or up to 4 hours.
02 - Combine all-purpose flour, panko breadcrumbs, and grated Parmesan cheese in a shallow dish. Beat the eggs in a separate bowl.
03 - Remove chicken from marinade. Coat each fillet in the flour mixture, then in beaten eggs, and once more in the flour mixture to ensure a thick, crispy crust.
04 - Fill a heavy skillet with 1/2 inch of vegetable oil and heat to 350°F. Fry chicken fillets for 3–4 minutes per side until golden brown and thoroughly cooked. Transfer to a plate lined with paper towels to drain excess oil.
05 - Toss shredded romaine with Caesar dressing in a mixing bowl. Gently fold in shaved Parmesan cheese.
06 - Spread unsalted butter on cut sides of buns and toast in a skillet until golden, if desired. Arrange fried chicken fillets on the bottom buns, top with Caesar salad, and cover with toasted top buns.
07 - Serve immediately. Offer additional Caesar dressing or lemon wedges on the side if desired.