Prepare the sauce ahead of time by combining all the ingredients for it in a saucepan. Bring to a simmer over a medium heat and allow it to reduce until slightly thickened. Remove from the heat and set to one side. Place the rice in a large saucepan with a little salt. Cover with the boiling water and bring to the boil. Reduce to a simmer, then cover with a lid and cook gently for 10-15 minutes until the rice is tender and has absorbed the water. Remove from the heat and keep covered with the lid to one side as you prepare the rest of the dish. Heat the groundnut oil in a wok set over a moderate heat until hot. Add the pork belly and stir-fry for 2 minutes. Add the prepared sauce and reduce the heat, cooking for 4-5 minutes, stirring occasionally until the meat is cooked through with no pink showing. Fluff the rice with a fork and spoon into serving bowls. Add the pineapple to the pork and stir well. Sit the rice bowls on serving plates and spoon the pork around them. Garnish with a sprig of coriander before serving.