For the chicken: Place the chicken thighs in the bottom of a 5-6 quarter slow cooker.
In a mixing bowl or large measuring cup, whisk together the ketchup, bourbon, maple syrup, apple cider vinegar, molasses, mustard, Worcestershire, onion powder, garlic powder, and red pepper flakes. Pour over the chicken. Cover and cook for 2 hours on high or 4-6 hours on low, until the chicken is cooked through. Transfer to a large bowl or plate and shred with two forks.
While the chicken cooks, prepare the slaw. Place the broccoli slaw, scallions, and apple in a large mixing bowl. In a separate bowl or large measuring cup, whisk together the Greek yogurt, apple cider vinegar, maple syrup, mustard, salt, and pepper until smooth. Pour over the slaw, toss to coat evenly, then refrigerate for 2 hours or up to 1 day. (The slaw tastes best when allowed to sit in the refrigerator for a few hours.)
Assemble the sandwiches: Spread the buns with Dijon mustard (optional). Pile the shredded chicken onto the bottom bun, top with slaw, then add the top bun. Enjoy warm.
Leftover BBQ chicken can be refrigerated up to 4 days. Reheat gently on the stove. Leftover slaw can be refrigerated 2-3 days, but tastes best the first day (after 2 or so hours in the refrigerator to allow the flavors to meld) or the second day.
Gourmet Sandwich Recipe, Maple Bourbon BBQ Chicken Sandwiches with Apple Slaw, Slow Cooker Chicken