Spatchcock the chicken by cutting down both sides of the spine with a pair of kitchen scissors. Flatten the chicken out by leaning the heel of your hand on the chicken and press down to crack the breastbone. Keep the backbone to make soup stock.
Season the chicken with the salt and pepper to taste and rub in the curry powder.
Mix the marinade ingredients in a large bowl (large enough for the flattened chicken, or a baking pan) and coat the chicken by turning it over several times to ensure it is covered by the marinade. Cover the bowl and refrigerate for at least 2 hours.
With a heated grill, move hot coals to one side, and place the flat chicken, breast side up, on the grill where there is no coals (indirect heat), baste with marinate and cover grill for 20-25 minutes.
Turn the chicken over and baste again, cover and continue barbecuing for another 15-20 minutes.
Pierce the chicken in a thick part of the thigh to check for juices running clear or use a meat thermometer and look for a target temperature of 75 C or 165 F. When juices are clear or the correct temp, remove from the grill and let rest for 5 minutes.