Place the rice in a large saucepan and cover with the stock. Add salt and the turmeric and stir well. Bring to the boil over a moderate heat then cover with a tight-fitting lid and reduce to a gentle simmer. Cook for 15-20 minutes until the rice is tender.
Remove from the heat and set to one side, still covered by the lid, for at least 10 minutes. After 10 minutes, heat the groundnut oil in a large frying pan or wok over a high heat until hot. Stir-fry the prawns for 3-4 minutes until pink and tender.
Stir through the pineapple and remove from the heat, seasoning to taste. Fluff the rice using a fork then stir it into the prawns and pineapple. Spoon into wicker serving glasses. Garnish with the spring onion before serving.