Begin by making the Pickled Slaw: In a large bowl mix together the vinegar, sugar, and salt. Add the veggies and stir well.
Next make the Gochujang Mayonnaise: Mix all the ingredients together in a small bowl.
Then, fry the chicken: Cut each breast in half horizontally, and then flatten each of the four pieces, between two sheets of plastic wrap, with a rolling pin or meat tenderizer.
In a cast iron Dutch oven, or other heavy pot, heat about one inch of oil until it reaches 350 degrees.
As the oil heats, prepare your dredging station. Fill one bowl with the buttermilk and gochujang. Divide the flour and spices between two bowls.
Dip each piece of chicken into the first bowl of flour, then in the buttermilk, and then back in the flour. When the oil reaches 350 degrees, fry the chicken two pieces at a time until they are golden brown on both sides. They will cook for about 7 minutes. Do not add the second batch of chicken until the oil reheats to exactly 350 degrees. Drain all the chicken on a wire rack.
To assemble the sandwiches: Spread the buns with the Gochujang Mayonnaise and top with the chicken and slaw.