01 - Slice each chicken breast in half horizontally to create 4 thin fillets of even thickness.
02 - Whisk together buttermilk, garlic powder, onion powder, salt, and pepper in a bowl. Submerge chicken pieces and marinate for at least 15 minutes, or refrigerate up to 4 hours for maximum flavor penetration.
03 - Prepare three separate bowls: one with flour, one with beaten eggs, and one combining panko breadcrumbs with grated Parmesan cheese.
04 - Remove chicken from marinade. Dredge each piece in flour, shaking off excess. Dip into egg wash, then press firmly into panko-Parmesan mixture to coat completely and evenly.
05 - Heat ½ inch of vegetable oil in a large skillet over medium-high heat. Fry chicken pieces for 3–4 minutes per side until golden brown and internal temperature reaches 165°F. Transfer to paper towels to drain.
06 - Lightly toast brioche buns until golden and warm throughout.
07 - Spread Caesar dressing on the bottom half of each bun. Layer with shredded romaine lettuce, a crispy chicken fillet, additional Caesar dressing, and shaved Parmesan. Finish with freshly ground black pepper.
08 - Place top bun on each sandwich and serve immediately while chicken remains crispy.