Purée half the chopped pineapple and add pepper. Heat a little oil in a saucepan and fry red curry paste, palm sugar and peppered pineapple for a few minutes, or until fragrant.
Add coconut milk and stock and bring to the boil. Simmer on low heat for 10 minutes, uncovered.
Add remaining chopped pineapple and simmer for 5 minutes. Add prawns and fish s