Use a sharp knife to score the lamb leg in fi ne parallel lines, then season generously with salt and pepper. Rub with the za-atar and 1 Tbsp extra virgin olive oil. Cook on a moderate barbecue grill for 20-25 minutes, turning several times, until medium. Set aside to rest.
Blanch the peas in a saucepan of rapidly-boiling salted water for 1 minutes, then refresh in iced water. Drain, then mix with the herbs and remaining olive oil in a food processor and purée until smooth. Season with salt, then stir in the shallots.
Peel halve and seed the cucumber, then grate coarsely. Season with salt, stand for 2 minutes, then squeeze to remove excess moisture. Mix with the yoghurt, garlic, zest and juice. Scatter with the sumac. Serve with the peas, carrots and carved lamb.