01 - Combine chicken, pickle brine, and hot sauce in a resealable bag or bowl. Marinate in refrigerator for at least 1 hour, up to overnight.
02 - Heat vegetable oil in a heavy-bottomed pot or deep skillet to 350°F.
03 - Whisk together flour, cornstarch, paprika, garlic powder, onion powder, cayenne pepper, kosher salt, and black pepper in a shallow dish.
04 - Remove chicken from brine, allowing excess liquid to drip off. Dredge each piece thoroughly in the flour mixture, ensuring complete coverage on all sides.
05 - Fry chicken pieces in batches for 5-7 minutes per side until golden brown and cooked through, reaching an internal temperature of 165°F. Drain on wire rack or paper towels.
06 - Mix mayonnaise and Dijon mustard in a small bowl until smooth and well combined.
07 - Lightly toast the buns and spread the mayo-mustard sauce on both cut sides.
08 - Layer fried chicken, shredded lettuce, and pickle slices onto the bottom buns. Cover with top bun halves and serve immediately.