In a small bowl, combine the minced garlic, olive oil, ground cumin, ground coriander, ground paprika, ground turmeric, ground cinnamon, ground black pepper, salt, lemon juice, chopped parsley, and chopped cilantro. Mix well to form a paste.
Rinse the leg of lamb and pat it dry with paper towels. Using a sharp knife, make small slits all over the lamb.
Rub the marinade paste all over the lamb, ensuring it gets into the slits. Cover the lamb with plastic wrap and refrigerate for at least 4 hours or overnight for best results.
Preheat your grill to medium-high heat. If using a charcoal grill, ensure the coals are hot and have a layer of white ash.
Place the marinated leg of lamb on the grill. Cover the grill and cook for about 1.5 to 2 hours, turning occasionally to ensure even cooking.
The lamb is done when it reaches an internal temperature of 145째F (63째C) for medium-rare or 160째F (71째C) for medium. Use a meat thermometer to check for doneness.
Once cooked to your desired doneness, remove the lamb from the grill and let it rest for about 15 minutes before carving. This allows the juices to redistribute throughout the meat.
Carve the mechoui into slices and arrange on a serving platter. Garnish with additional fresh parsley and cilantro if desired.
Enjoy your meal!