01 - Whisk buttermilk, Cajun seasoning, smoked paprika, garlic powder, onion powder, cayenne, salt, and pepper in a bowl. Submerge chicken breasts, cover, and refrigerate for 30 minutes to 4 hours.
02 - Combine mayonnaise, minced garlic, lemon juice, Dijon mustard, salt, and pepper in a small bowl. Mix thoroughly and refrigerate until assembly.
03 - Blend flour and cornstarch in a shallow dish. Remove chicken from marinade, allow excess to drip off, and coat each piece in flour mixture, pressing gently to ensure even coverage.
04 - Heat 1 inch of vegetable oil to 350°F in a large skillet or Dutch oven. Fry chicken breasts for 5–7 minutes per side until golden brown and internal temperature reaches 165°F. Drain on wire rack.
05 - Spread garlic aioli on cut sides of toasted buns. Layer lettuce on bottom half, add fried chicken, tomato slice, and pickles. Place top bun and serve immediately.