1. Heat a large nonstick skillet over medium-high heat. Add half of lamb to pan. Cook 5 minutes or until browned, stirring occasionally. Place lamb in a 5-quart electric slow cooker. Repeat procedure with remaining lamb.
2. Add coriander, onion, and tomatoes to slow cooker. Cover and cook on LOW for 7 hours.
3. Add olives. Turn off slow cooker; let stand, covered, 30 minutes.
4. Place couscous in shallow bowls. Spoon lamb mixture over couscous. Garnish with preserved lemon and cilantro, if desired.
Ingredient Tip: Preserved lemons are lemons that have been pickled in salt; their juices appear often in Middle Eastern and Mediterranean cuisines. You can purchase them at specialty markets.