Preheat oven to 200C (400F). In a bowl, mix half the oil with herbs, garlic and lemon zest.
Heat a large frying pan over high heat. Coat lamb in remaining oil and sear until golden on both sides. Transfer to a baking dish and rub her mixture into rack.
Add onions to dish and bake for 25 minutes. Remove meat from oven, cover loosley with foil and set aside to rest for 10 minutes.
Bring a large saucepan of lightly salted water to a boil.
Cook carrots for 2 minutes, then add beans and peas and cook for a further 4 minutes. Drain and serve with lamb.