In a bowl, combine minced garlic, ground cumin, coriander, paprika, turmeric, black pepper, cinnamon, salt, olive oil, and lemon juice. Mix well to form a paste.
Rub the marinade paste all over the lamb, making sure to get it into all the crevices. Cover and refrigerate for at least 4 hours or overnight for best results.
Preheat your grill to medium-high heat. If using a charcoal grill, prepare the coals and let them burn until they are covered with a layer of gray ash.
Place the marinated lamb on the grill. Cook, turning occasionally, for about 1.5 to 2 hours, or until the lamb is cooked through and has a nice char on the outside. The internal temperature should reach 70°C (160°F) for medium doneness.
Once cooked, remove the lamb from the grill and let it rest for about 15 minutes before carving.
Garnish with fresh herbs if desired. Serve the Mechoui with flatbreads or couscous.
Enjoy your meal!