For the marinade: Put the chicken in a large bowl and add the buttermilk, hot sauce, salt, Cajun seasoning, garlic powder, paprika and black pepper and toss until the chicken is coated. Refrigerate for 4 hours or up to overnight.
For the seasoned flour: Combine the flour, Cajun seasoning, pepper, baking powder, salt and confectioners' sugar in a large shallow dish or paper bag.
Remove the chicken from the buttermilk and dredge each piece in the seasoned flour. Shake off any excess and transfer to a plate.
Fill a large cast-iron skillet halfway with oil and fit the skillet with a deep-frying thermometer. Heat to 350 degrees F. Line a baking sheet with paper towels and set a cooling rack on top.
Add 5 or 6 pieces of chicken at a time to the oil and cook for 3 to 4 minutes, then flip and cook until the chicken is golden brown and juices run clear when pierced, 3 to 4 minutes more.
Remove to the prepared cooling rack and let sit for 5 minutes. (See Cook's Note.)
For the sandwiches: Meanwhile, mix together the mayonnaise, Dijon, pickle brine and hot sauce in a small bowl. Spread the mixture on both sides of the baguettes. Lay the pickles and tomatoes on top of the mayonnaise on one side of each piece of bread. Add a few chicken pieces to each. Top with some Red Cabbage Slaw and the top pieces of bread. Cut each loaf in half, then cut into 8 to 10 portions. Serve with lots of napkins!
Red Cabbage Slaw:
Combine the oil, vinegar, Dijon mustard, granulated sugar, mustard seeds and minced garlic in a bowl and whisk together. Add the coleslaw mix, cabbage and green onions and toss lightly. Taste the slaw, then add salt and pepper to your liking. Serve right away or chill up to overnight.
If not serving the chicken immediately, hold it in a 200 degree F oven on the prepared rack for up to 30 minutes.