Marinate the Chicken
Place the chicken breasts in a bowl with the buttermilk. Cover and let marinate in the fridge for at least 30 minutes (or up to overnight) to tenderize and flavor the chicken.
Prepare the Coating
In a mixing bowl, combine the flour, garlic powder, onion powder, paprika, salt, and pepper. Remove the chicken from the buttermilk, letting the excess drip off, and dredge it in the seasoned flour mixture until well-coated.
Fry the Chicken
Heat about 1 inch of oil in a large skillet over medium-high heat until it reaches 350°F (175°C). Fry the chicken pieces for 4-5 minutes per side, or until golden brown and fully cooked (internal temperature of 165°F). Place the fried chicken on paper towels to drain excess oil.
Make the Caesar Dressing
In a small bowl, whisk together the mayonnaise, Parmesan cheese, lemon juice, minced garlic, Dijon mustard, salt, and pepper until smooth. Adjust seasoning as needed.
Assemble the Sandwiches
Toast the sandwich buns or bread slices if desired. Spread Caesar dressing on the bottom half of each bun. Layer with a piece of fried chicken, romaine lettuce, and shredded Parmesan cheese. Top with the other half of the bun.
Serve and Enjoy
Serve the sandwiches immediately, with extra Caesar dressing on the side for dipping if desired.