In a large, zip top bag, combine olive oil, garlic, lemon zest, ginger, paprika, coriander, cumin, black pepper, cayenne pepper, cloves, saffron, cinnamon stick, salt and lamb. Seal well, pressing out excess air. Refrigerate 4-6 hours, turning occasionally.
Empty the bag into a tagine or a medium enameled cast-iron casserole. Remove the lemon zest and discard. Add the water, carrots and onion, and bring to a simmer. Cover and cook over low heat 2 hours or until lamb is quite tender.
Remove fat from broth. Rinse olives well and add to pan. Season with salt to taste. Remove from heat and add parsley, cilantro and lemon juice. Serve with couscous.