Whisk together the sesame oil, lemon juice, half the ginger and 1 tbsp of the chopped mint in a shallow dish. Add the lamb and stir well, then cover and leave to marinate while preparing the remaining ingredients (or, if time allows, marinate for 2–3 hours in the fridge).
Put the potatoes in a large pan 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 over 1 tbsp of the vegetable oil and gently toss to coat. (This will stop the potatoes from sticking together when stir-fried.)
Heat 1 tbsp 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 pan and, when hot, add the sliced courgettes. Stir-fry for 1 minute, then add the potatoes. 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 moderate 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 and scatter over the remaining chopped mint, then serve.
For a pork and pear stir-fry, use 350g lean pork fillet. Instead of courgettes, quarter and slice 2 firm but ripe pears, preferably red-skinned; add them after the potatoes, at the same time as the spring onions. * For a vegetarian dish, replace the lamb with a packet of tofu, about 350g, cut into bite-sized cubes. Marinate in a mixture of 2 tsp toasted sesame oil, 1 tbsp soy sauce, 1 tbsp mirin (Japanese rice wine) or sherry, 1 crushed garlic clove and 1 tbsp finely chopped fresh root ginger.