Preheat oven to 220°C. Place pork into a roasting pan. Rub the oil, then salt over pork skin. Roast for 1 hour then reduce temperature to 180°C. Roast for a further 1 hour or until cooked through when tested with a skewer or meat thermometer.
Meanwhile, to make sauce, cut roots and 4cm of coriander stalks and finely chop. Heat oil in a saucepan over medium heat. Add coriander, onion, chilli and ginger. Cook for 3 minutes or until softened.
Drain juice from one can of pineapple and discard. Add pineapple to saucepan with other can of pineapple and juice. Add sugar. Stir until sugar dissolves and mixture comes to the boil. Add fish sauce and lime juice and simmer for 20 minutes or until sauce is slightly thickened. Transfer to a serving bowl and cool. Serve pork with pineapple sauce and vegetables of choice.