1. Combine lamb, garlic, ginger, cinnamon, nutmeg and 1 tsp. salt in a large bowl. Cover and refrigerate for at least 1 hour, or up to 12.
2. Place lamb in a slow cooker; add carrots and 2 cups chicken broth. Cover and cook on low until lamb is fork-tender, about 6 hours.
3. In a large saucepan, bring remaining 2 cups broth and 1/2 tsp. salt to boil. Add couscous, stir, cover and remove from heat. Let stand 5 minutes, fluff with a fork, and transfer to a large serving bowl. Spoon lamb and skimmed juices over couscous and sprinkle with parsley. Serve immediately.