Whisk together the sesame oil, lemon juice, half the ginger and 1 tablespoon of the chopped mint in a shallow dish. Add the lamb and stir well, then cover and leave to marinate while you prepare the remaining ingredients.
Put the potatoes in a large saucepan and pour over enough boiling water to cover them. Bring back to the boil, half-cover the pan with a lid and simmer for 12 minutes or until almost tender when pierced with the tip of a sharp knife. Drain and leave until they are cool enough to handle. Cut across into slices slightly thicker than 5mm, then cut the slices into sticks. Put them in a bowl, drizzle with 1 tablespoon of the vegetable oil and gently toss to coat. (This will stop the potatoes from sticking together when stir-fried.)
Heat 1 tablespoon of the remaining oil in a wok or large frying pan. When the oil is hot, add the lamb and stir-fry over a high heat for 1 minute or until just browned, but still fairly rare. Quickly remove and set aside.
Add the remaining oil to the wok and, when hot, add the sliced zucchini. Stir-fry for 1 minute, then add the potato sticks. Cook for 3–4 minutes, stirring all the time, until lightly browned, taking care not to break up the potatoes. Add the spring onions and cook for 1 more minute, stirring.
Reduce the heat to medium and add the peas, soy sauce, stock, honey and remaining ginger. Return the lamb with any juices. Stir-fry for 2–3 minutes or until the liquid is bubbling and everything is tender and hot. Season to taste, scatter the remaining chopped mint over the top, then serve.