How to Make It
Preheat the oven to 350°. Put the garlic on a double piece of foil and drizzle with olive oil. Wrap the garlic in the foil and bake for about 1 hour and 15 minutes, until very soft.
Squeeze the garlic cloves into a bowl and mash with a fork. Stir in the lemon zest, lemon juice, paprika, cumin, coriander, cinnamon and the 2 tablespoons of olive oil. Add 1 teaspoon of salt and 1/2 teaspoon of black pepper.
Lay the lamb on a work surface and make 1/2-inch-deep slits all over the meat. Transfer the lamb to a rimmed baking sheet and spread the spice paste all over, rubbing it into the meat. Cover and refrigerate overnight.
Light a grill. Bring the lamb to room temperature and season with salt and pepper. Grill the lamb fat side down over moderately high heat until charred, about 20 minutes. Turn the lamb and grill for about 20 minutes longer, until an instant-read thermometer inserted in the thickest part registers 130° for medium meat. Transfer the lamb to a work surface to rest for about 15 minutes.
Carve the lamb into thin slices and serve it with grilled flatbread, dilled yogurt and sliced cucumbers.