To prepare the teriyaki sauce: Mix the sauce ingredients together in a small bowl and set aside. To cook the vegetables: Heat a little oil in a large, non-stick frying pan or wok, add the vegetables and stir-fry for 3-4 minutes. Remove to a plate and keep warm while you cook the lamb. To cook the lamb: Add a little more oil to the hot pan or wok. Add half the lamb and stir-fry for 3-4 minutes. Remove from the pan and keep warm while you cook the rest of the lamb. Combine all the lamb and the vegetables in the pan or wok and toss to combine. Stir through the teriyaki sauce and cook for a further 2-3 minutes. Taste and season.