Preheat the oven to 180°C. Place the lamb in a roasting dish, brush lightly with oil and season with salt and pepper. Toss the vegetables with the oil and rosemary sprigs and set aside.
Place the lamb in the oven. Roast for 1 hour for rare, 1 hour 15 minutes for medium, or 1 hour 30 minutes for well done. After the first 40 minutes of cooking time, add the vegetables around the lamb in the roasting dish and continue to cook.
Remove the lamb, cover loosely and allow to rest for 15 minutes before carving. Serve the lamb with roasted vegetables.