After removing the shells from the prawns, place the shells in a medium pot with a sprinkle of sea salt. Bring to the boil and cook for 5-10 minutes. The water - stock will change the colour.
Strain the shells through a sieve, keeping the stock.
Place the stock back in a medium pot.
Add the ginger, chilli, soy sauce, prawns, mange tout, red pepper and carrot and half of the green spring onion. Cook for a few minutes only, until the prawns are nearly cooked. Then add the rice noodles, which need very little to cook (follow the manufacturer’s instructions). When they are cooked, pour the coconut milk and mix it in. Add the green spring onion and coriander (remaining some to sprinkle in the bowl) and mix well.
Serve in a bowl, with a sprinkle of chopped green spring onion and a fresh coriander.