For the crisp pork belly, pierce the rind side of pork with a sharp fork or knife until the skin is covered with fine holes. Insert a meat hook into the meat to secure it.
Bring a large pan of water to a boil and, using a large ladle, pour the hot water over the rind side of the pork several times. This is best done suspending the pork above the sink. Set the pork belly aside.
Heat a wok until it is hot, then add the salt, both peppers, five-spice powder and sugar and stir fry the mixture for three minutes. Allow the mixture to cool slightly.
When the mixture is cool enough to handle, rub it into the flesh side of the pork. Hang the meat to dry for eight hours or overnight in a cool place or in front of a fan. Alternatively, place the meat on a wire rack set above a roasting tin.
Preheat the oven to 200C/400F/Gas 6. Place the pork on a wire rack, rind-side up, over a deep roasting pan filled about one third with water and roast for 20 minutes.
Reduce the heat to 180C/350F/Gas 4 and continue to roast for two hours. Turn the oven back up to 230C/450F/Gas 8 and cook for 15 minutes. Remove the meat from the oven and allow the pork to cool.
For the Chinese greens, heat a wok and add the oil. Once hot, add the scallions cook for 1-2 minutes. Add the bok choi, chili and three tablespoons of water and cook for a further 2-3 minutes.
Add the sesame oil and mix to coat the vegetables. To serve, carve the pork into bite-sized pieces, arrange on a platter and serve with the Chinese greens.