1) Preheat heat the oven to 220C/200C fan/gas 7. 2) To make the marinade, mash the 4 garlic cloves to a paste using a pestle and mortar. Mix with the olive oil, lemon juice, oregano and thyme leaves, and season. 3) Butterfly the lamb, or ask your butcher to do it. Place in a large dish. 4) Pour the marinade over the lamb and massage well into the meat. 5) Leave the lamb to marinate for at least 1 hr or longer in the fridge, but no longer than overnight. 4) Place the lamb in a shallow roasting tin and roast for 30 mins for pink or 40 mins for well done, turning halfway through. 5) Leave the meat to rest for 10 mins before carving. 6) Meanwhile, make the tzatziki. Grate the cucumber, sprinkle with a pinch of salt and squeeze out all the liquid. Mix with the yogurt, garlic and mint. 7) Carve the lamb into thick slices and serve with the tzatziki wrapped up in warm flatbreads.