1. Prepare the marinade
Place all marinade ingredients into a blender and blend until smooth.
2. Marinate the lamb
Place the lamb leg in a large tray or dish. Pour over the marinade and rub it thoroughly over the lamb, ensuring it is evenly coated. Cover and refrigerate for at least 1 hour, or overnight for best results.
3. Preheat the oven
Preheat the oven to 200°C.
4. Roast the lamb
Arrange the vegetables in a large roasting tray and place the marinated lamb on top. Cover the tray with baking paper, then seal tightly with foil.
Roast for 3–4 hours, or until the lamb is tender and the meat easily pulls away from the bone.
Increase the oven temperature to the highest setting. Remove the foil and baking paper, then return the lamb to the oven for a further 10 minutes, or until golden and caramelised.