Heat a nonstick wok or large saucepan over a high heat and then add the oil. Stir in the garlic, ginger, red chillies and spring onions. Stir-fry for 30 seconds and then add the coconut milk, lemon grass, soy sauce, lime rind and juice, and sugar. Bring to the boil then add the clams.
Bring back to the boil, cover and cook briskly for 3–5 minutes or until all the clams have opened. Discard any that remain closed.
Remove from the heat, stir in the coriander and season well. Ladle into warmed bowls and serve immediately with a spoon for the juices.