01 - Combine chicken, pickle brine, and hot sauce in a resealable bag or bowl. Refrigerate for at least 1 hour, up to overnight.
02 - Heat vegetable oil in a heavy-bottomed pot or deep skillet until it reaches 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 to drip off. Press each piece firmly into the flour mixture, turning to coat all sides evenly.
05 - Fry chicken in batches for 5–7 minutes per side until golden brown and internal temperature reaches 165°F. Transfer to a wire rack to drain.
06 - Stir together mayonnaise and Dijon mustard in a small bowl until smooth.
07 - Lightly toast the cut sides of the buns until golden.
08 - Spread mayo-mustard sauce on both bun halves. Layer fried chicken, shredded lettuce, and pickle slices on the bottom buns. Cover with top buns and serve immediately.