Wash the clams under cold running water, discarding any that are broken or that remain open when tapped. Soak them in plenty of cold water for 30 minutes, then drain and rinse again in cold running water. Place in a bowl, cover with a wet tea towel and keep refrigerated until needed.
Heat the oil in a wok over a high heat until the oil starts to shimmer. Add the garlic and ginger and stir-fry for a few seconds. Add the clams and all the remaining ingredients, reserving the 1 sliced chilli to garnish. Cook, stirring, for 4–5 minutes until the clams open. Serve immediately, discarding any clams that remain closed. Garnish with slices of red chilli.