Toss the prawns with the turmeric and half a teaspoon salt and set aside. Finely chopp half the tomatoes and cut the rest into wedges. Set aside.
Heat the oil in a large deep frying pan. Add the onions or shallots and fry for 5 minutes until soft and translucent.
Add the garlic, ginger, pandan and curry leaves and stir fry for a minute. Add the crushed dried chillies and pieces of cinnamon and stir fry for another 2 minutes until the mixture smell aromatic.
Add the finely chopped tomatoes, green chilli, leek, black pepper and 1 tsp salt and stir fry for 5 minutes.
Add the prawns, green pepper and tomato wedges and cook for another 5 minutes until the prawns are cooked. Stir in the lime juice, scatter over the mint leaves and serve.