2 tbsp sunflower oil
2 spring onions (scallions), thinly sliced diagonally
1 carrot, coarsely grated
125 g (4 1/2 oz) large closed cup mushrooms, thinly sliced
1 litre (1 3/4 pints) 4 cups fish or vegetable stock
1/2 tsp Chinese five-spice powder
1 tbsp light soy sauce
125 g (4 1/2 oz) large peeled prawns (shrimp) or peeled tiger prawns (shrimp), defrosted if frozen
1/2 bunch watercress, trimmed and roughly chopped
1 egg, well beaten
salt and pepper
4 large prawns (shrimp) in shells, to garnish (optional)