01 - Slice each chicken breast in half horizontally to create 4 thin fillets of even thickness.
02 - Whisk buttermilk, garlic powder, onion powder, salt, and pepper in a bowl. Add chicken and marinate for at least 15 minutes, or up to 4 hours in the refrigerator for optimal flavor absorption.
03 - Prepare three shallow bowls: one with flour, one with beaten eggs, and one with panko breadcrumbs mixed with grated Parmesan cheese.
04 - Remove chicken from marinade. Dredge each piece in flour, shaking off excess. Dip in beaten egg, then coat thoroughly with the panko-Parmesan mixture, pressing gently to adhere.
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 cooked through, reaching an internal temperature of 165°F. Drain on paper towels.
06 - Lightly toast the brioche or sandwich buns until golden and warm.
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 cheese. Season with freshly ground black pepper.
08 - Place the top bun on each sandwich and serve immediately while chicken is still crispy.