Trim an excess fat from the chicken. Pound each piece flat. I like to put them in a one gallon baggie and then pound them so the chicken doesn't splatter.
Whisk together the buttermilk, dressing, and seasoning. Pour into a large resealable container. Add the chicken and seal.
Refrigerate overnight.
For the slaw
Combine all but the dressing in a large bowl.
Drizzle dressing over the top of the slaw and stir to combine. Cover and refrigerate until ready to make the sandwiches,
For the batter
Heat 3" of vegetable oil in a Dutch oven or heat a deep fryer filled with oil to 375 F.
Whisk together the batter ingredients in a pie pan or shallow bowl.
Remove chicken from the brine and shake off any excess. Transfer to the batter mixture and coat well, turning to get all sides.
Place chicken in the oil and fry until internal temperature is 160-165 F, turning once. If you pounded the chicken very thin it won't take long to cook, 2-3 minutes per side. The coating will turn a lovely golden brown when it's done.
Remove pieces to a wire rack or paper towel-lined plate to drain.
For the sandwiches
Toast the buns if you wish.
Add a piece of chicken to each bun and top with plenty of the slaw and few pickle slices.