Heat the oil in a wok over a medium to high heat. When hot, add the galangal, ginger, garlic, lemon grass and chillies and stir-fry for 2 minutes. Sprinkle over the curry powder and turmeric, and continue to fry for 30 seconds before adding the lime leaves and tomatoes. Fry the mixture for 2-3 minutes, until the tomatoes begin to break down. Pour in the hot stock and the coconut milk. Give everything a stir, then bring the mixture to the boil. Reduce the heat and let the soup simmer for 10 minutes to allow the flavours to infuse.

Add the salmon chunks and the prawns to the soup with the fish sauce. Simmer gently for about 2 minutes, until cooked through.

Divide the noodles between serving bowls, pour over the hot laksa and scatter with coriander leaves, if using.