Cook the potatoes in boiling water for 15 minutes, until tender. Drain and return to the pan.
Finely chop half the coriander and add to the pan with the tomato and chili sauce and 6tbsp water. Bring to the boil,reduce the heat,cover and simmer gently for 5 minutes.
Stir in the prawns and heat briefly until they are warmed through. Do no overheat the prawns or they will shrivel,becoming tough and tasteless. Spoon into shallow bowls and serve spinkled with the remaining coriander,torn into pieces.