2.5 cm (1 inch) piece fresh root ginger, peeled and sliced
lime juice, to serve
Place the tom yum paste in a large saucepan with the stock and bring to a simmer. Add the mushrooms, spring onions, garlic and ginger and simmer for 5–6 minutes, so the flavours develop and the mushrooms soften.
Ladle into bowls and serve immediately with a squeeze of lime juice.