01 - In a bowl, whisk together buttermilk, garlic powder, onion powder, salt, and black pepper. Submerge chicken fillets in the marinade, cover, and refrigerate for at least 15 minutes or up to 4 hours to enhance tenderness.
02 - Combine flour, panko breadcrumbs, and grated Parmesan in a shallow dish. In a separate bowl, beat eggs until smooth.
03 - Remove chicken pieces from marinade and allow excess liquid to drip off. Dredge each fillet in the flour mixture, then dip in beaten eggs, and coat again in the flour mixture for an extra-crisp exterior.
04 - Pour vegetable oil into a large skillet to a depth of 1/2 inch and heat to 350°F. Fry chicken fillets for 3 to 4 minutes per side until golden brown and fully cooked. Transfer to a plate lined with paper towels to absorb excess oil.
05 - In a mixing bowl, toss shredded romaine lettuce with Caesar dressing. Add shaved Parmesan cheese and gently mix to combine.
06 - If desired, spread unsalted butter on the cut sides of buns. Toast in a hot skillet until golden brown. Arrange fried chicken on each bottom bun, top with Caesar salad, and cover with the top bun.
07 - Serve sandwiches immediately. Accompany with extra Caesar dressing or lemon wedges if preferred.