Prepare water bath for sous vide cooking to 148F.
Season chicken thighs with salt and pepper or your choice of seasoning; arrange in single layer in vacuum seal bag; seal.
Sous vide chicken for 3 hours.
Immediately place sealed chicken in 50/50 ice water bath; let chill for 15 minutes. Remove chicken from bags; pat dry with paper towels.
To prepare the batter, whisk tempura mix and salt on a plate.
Whisk buttermilk, egg and marinade in a bowl.
Dredge chicken in dry tempura mix then drop in buttermilk mixture to coat.
Spoon 3 to 4 tablespoons of buttermilk mixture into remaining dry tempura mix and stir with a fork forming small clumps.
Dredge chicken again in tempura mixture pressing so clumps adhere. Heat oil to 375F. in large skillet.
Fry chicken until golden brown and crispy; about 2 to 4 minutes.
Whisk dressing ingredients together and toss with broccoli slaw. Season with S&P
Cook buns in steamer basket until soft and heated through, about 5 to 8 minutes.
Open buns and spread inside with hoisin sauce.
Top with gingered slaw, chicken, pickled onions and cilantro.