Cut the pork in half lengthways. Using a sharp knife, cut slits into both sides of the pork in a crisscross pattern. Place the char siu sauce in a shallow glass or ceramic dish, add the pork and turn to coat evenly. Cover and leave to marinate in the refrigerator for 1 hour, or overnight if time permits.
Place a roasting rack or wire rack over a roasting tin. Pour cold water into the tin to a depth of 2.5 cm (1 inch). Lay the pork on the rack and drizzle with half the honey. Place the tin under a preheated high grill about 10 cm (4 inches) from the heat source and cook for 10–12 minutes until browned.
Turn the pork over, drizzle with the remaining honey and cook for 8–10 minutes until just cooked through. Remove from the grill, cover with foil and leave to rest for 12–15 minutes before thinly slicing. Serve with steamed rice and steamed Asian greens.