Preheat oven to 220°C/200°C fan forced. Cut 4 x 2cm deep cuts into under-side of pork. Place, skin-side up, in a roasting pan and rub with oil and sea salt. Roast in oven for 45 minutes.
Meanwhile, for the plum sauce, chop 2 of the plums and place in a small food processor. Add the sugar, orange rind, ginger and garlic. Process until combined and smooth. Pour the puree into a saucepan over medium heat. Add the stock, honey, orange juice, soy sauce, rice wine, sesame oil, cinnamon and star anise. Bring to the boil, then reduce heat to medium-low and simmer for 30 minutes or until reduced by half and thickened to a smooth sauce.
Pour mixture around pork, taking care not to cover skin. Add remaining plum halves around the pork and return to oven to roast for a further 30 minutes or until pork is cooked through and crackling is crisp.
Transfer pork to a chopping board. Stand for 5 minutes then thinly slice. Serve with sauce and plums from roasting pan, rice and green onion.