Cook the noodles according to the packet instructions. While they are cooking, heat the oil in a wok or large saucepan and briefly fry the garlic and chilli. Stir in the peanut butter and coconut milk to make a loose paste before adding the stock. Bring to a simmer and add the prawns, spring onion, and soy sauce. Cook for 2 to 3 minutes until the prawns are heated through, and then add the cooked and drained noodles.Return to a simmer and finally add a squeeze of lime juice and the fresh coriander. Serve straight away.