The lamb is meant to be somewhat chewy and tangy with the lemon juice and sumac, making an extraordinarily delicious meal out of your hummus plate. Serve with pita bread.
To make the hummus, in the bowl of the food processor, puree the chickpeas and garlic clove. Stop and scrape down the bowl as you go, processing for several minutes until everything is completely pureed. This mixture may be very thick and ball up in the processor, depending how much liquid may be left in the cooked chickpeas.
Add the tahini, lemon juice, and a pinch of salt. Process, taste, and add more salt or lemon juice to adjust texture and taste as needed.
To make the lamb, cut the lamb shoulder into 1-inch pieces, cutting away excess fat and gristle.
In a medium bowl, combine the lamb with the lemon juice, minced or grated garlic, salt, and one tablespoon of the sumac. Stir well and let the mixture rest for 30 minutes at room temperature.
In a large sauté pan, heat the oil over medium high heat until hot but not smoking. Drain the meat and pat it lightly with a paper towel to dry it off so that the meat will brown properly.
Add the meat to the pan and sauté over high heat until the meat is completely browned and caramelized, 5-10 minutes. Season with the remaining tablespoon of sumac and cinnamon. Taste and adjust seasonings to taste.
Spoon the hummus onto 6 plates and make a well in the center of each with the back of a spoon. Place a spoonful of the lamb on top of each plate, and garnish with pine nuts, herbs, and a drizzle of olive oil. Serve immediately.