01 - Combine chicken, pickle brine, and hot sauce in a resealable bag or bowl. Refrigerate for at least 1 hour, up to overnight.
02 - Pour vegetable oil into a heavy-bottomed pot or deep skillet. Heat to 350°F.
03 - Whisk together flour, cornstarch, paprika, garlic powder, onion powder, cayenne pepper, salt, and black pepper in a shallow dish.
04 - Remove chicken from brine, allowing excess liquid to drip off. Press firmly into flour mixture, turning to coat completely on all sides.
05 - Fry chicken in batches for 5-7 minutes per side until golden brown and internal temperature reaches 165°F. Transfer to wire rack to drain.
06 - Stir together mayonnaise and Dijon mustard in a small bowl until fully combined.
07 - Lightly toast buns and spread mayo-mustard sauce on both cut sides.
08 - Place fried chicken on bottom bun, layer with lettuce and pickle slices, and top with remaining bun half. Serve immediately.