Heat oil in heavy large Dutch oven over low heat.
Add leeks and garlic. Cover and cook until leeks are very tender but not brown, stirring occasionally, about 10 minutes.
Add stock and next 7 ingredients. Season with salt and pepper. Increase heat and bring mixture to boil. Cover, reduce heat to medium and simmer until vegetables are crisp-tender, about 5 minutes.
Mix in tomatoes, garbanzo beans, cilantro, then couscous.
Remove from heat. Cover and let stand 10 minutes.
Fluff couscous with fork. Stir in raisins.
Transfer to large platter. Garnish with lemon wedges. Serve, passing Chunky Onion Harissa separately.