For the chicken: Mix together the hoisin, honey, soy, five-spice powder, crushed red pepper and sesame oil in a bowl. Pour half of marinade over the chicken in a plastic bag and marinate for 3 to 4 hours in the refrigerator, turning once halfway through. Reserve the remaining marinade.
For the pickled cabbage: Bring 1/2 cup water, the vinegar, sugar and salt to a boil until the sugar and salt are dissolved. Remove from the heat and add the carrots, crushed red pepper and cabbage. Stir to combine and let sit for at least 30 minutes. Pour into a bowl and let cool completely.
For the mustard: Whisk together the mustard powder, water, honey, oils and salt in a bowl until smooth.
For cooking and assembly: Heat a gas or charcoal grill to medium heat. Coat the grill with vegetable oil. Grill the chicken thighs until no longer pink in the middle and the internal temperature is 165 degrees F, 8 to 10 minutes per side. Let rest for 5 minutes, and then chop, toss with the marinade and coat in the sesame seeds.
Butter and grill the buns on both sides until golden brown, 1 to 2 minutes. Place ample quantities of glistening chicken on the bottom buns, then a drained handful of pickled cabbage and carrots, and top with hot mustard.