Combine all the marinade ingredients together in a bowl. Pour 3 tablespoons of the marinade into a small bowl for a serving sauce.
To secure the legs and wings in place, tie the duck with cooking string. This will create an even shape for cooking.
Place the duck in a dish, coat with three-fourths of the remaining marinade, and reserve the remaining one-fourth marinade to baste the duck. Cover with plastic wrap and refrigerate for at least 30 minutes or up to 2 hours.
Prepare the barbecue for indirect cooking over medium heat (180° to 230°C) with a rotisserie. If using a Weber Q barbecue, set up your barbecue with a convection tray and a trivet. Follow your rotisserie user's guide for specific set up instructions.
Slide one rotisserie fork onto the rotisserie rod. Slide the duck onto the rotisserie rod and secure with the second fork. Centre the duck on the rotisserie rod and tighten the forks.
Once the barbecue is preheated, set the duck and rotisserie rod in place. Turn on the rotisserie motor and ensure it is smoothly rotating.
Roast the duck over indirect medium heat, with the lid closed, until cooked through, 1 to 1¼ hours. Baste the duck two times with the reserved marinade. The final internal temperature for duck is 74°C, keep in mind the temperature will continue to rise 3° to 6°C while resting. Wearing heatproof gloves, remove the duck from the barbecue and allow to rest for 10 minutes.
Roast the duck over medium heat, with the lid closed, until cooked through, 1 to 1¼ hours. Baste the duck two times with the reserved marinade. The final internal temperature for duck is 74°C, keep in mind the temperature will continue to rise 3° to 6°C while resting. Wearing heatproof gloves, remove the duck from the barbecue and allow to rest for 10 minutes.
Once the duck has rested, carve into thin slices. Assemble the steamed bao buns with the sliced duck, cucumbers, coriander, bean shoots, chillies, spring onions, Sriracha, and finish with a drizzle of the reserved sauce.
