Ask your butcher to butterfly a leg of lamb for you, making it as flat as possible in order to grill evenly. Once you get it home, you can pound it to a more uniform thickness. But don’t worry if it’s not completely flat. The thicker parts will be medium-rare when cooked, and the thinner sections will be medium for those guests who don’t like their meat pink. 

To prepare the marinade, in a large, heavy sealable plastic bag, combine the olive oil, lemon juice, garlic, cumin, cardamom, salt, black pepper and Aleppo pepper. Add the lamb, seal the bag and refrigerate overnight or preferably for 2 days, turning the bag occasionally. 

Preheat a gas grill to medium-high heat, or prepare a medium-hot fire in a charcoal grill. 

Place the lamb on the grill, close the grill lid and cook, turning once, for 8 to 10 minutes per side for medium-rare. Transfer the lamb to a carving board, cover loosely with aluminum foil and let rest for 10 minutes.

While the lamb is cooking, prepare the onions and peppers. 

To prepare the onions, cut the onions in half lengthwise. Place the onions, cut side down, on a cutting board and cut crosswise into thin slices. 

In a large sauté pan or frying pan over medium heat, warm the olive oil until shimmering. Reduce the heat to low, add the onions and cook, stirring occasionally, until caramelized, about 20 minutes. Remove from the heat and set aside. 

To prepare the peppers, cut the bell peppers in half lengthwise; discard the seeds and veins. Cut the peppers lengthwise into 1/2-inch strips. 

In a large sauté pan or frying pan over medium-high heat, warm the olive oil until shimmering. Add the bell peppers, salt and black pepper and cook, stirring occasionally, until crisp-tender, 5 to 7 minutes. Remove from the heat and set aside. 

To prepare the tahini-yogurt sauce, in a medium bowl, whisk together the tahini, lemon juice and olive oil until smooth. Whisk in the yogurt, then the cumin, salt and Aleppo pepper. If not using immediately, cover and refrigerate for up to 2 days. Stir in the parsley just before serving.

To serve, while the lamb is resting, wrap a stack of pita breads in aluminum foil, place on the grill, close the grill lid and heat until warmed. 

Cut the lamb into thin slices. Place a warm pita on each plate. Top with several slices of lamb, then caramelized onions and then peppers. Drizzle the tahini-yogurt sauce over the top and serve.