Heat a small amount of olive oil in a deep frying pan, over a medium heat. Add the finely chopped onion and fry for 3-4 minutes until it is turning translucent. Reduce the heat slightly; add the coriander seed, black pepper, crushed garlic clove, and finely sliced lemongrass, and fry for a further 2 minutes. Now stir in the curry powder, turmeric and saffron strands, and pour in the coconut milk.
Once the coconut milk is gently simmering, mix in the zest and juice of a lime, and the raw prawns. Stir everything together and simmer for 2 or 3 more minutes, or until the prawns have turned pink. Remove from the heat, chuck in the bean sprouts, and serve in bowls with rice noodles or rice, a few thin slices of chilli, a sprinkling of coriander leaves, and a wedge of lime.