1. Depending on the size of the choi heads, either cut them in half lengthways or cut off the ends and separate the leaves.
2. Heat the olive oil over a high heat in a wok or large frying pan. Add the spring onions, chillies, garlic, ginger, fennel seeds and pak choi. Stir fry for 2 mins, then add the soy sauce and stock or water. Bring to the boil, then lower the heat and simmer for 2 mins. Dress with the sesame oil before serving.