Heat the olive oil in a large Dutch oven over medium heat. When the oil is shimmering, add the onions and sauté, stirring often, until translucent, about 8 minutes.
Add the carrots and sauté for another 5 minutes, until vibrant.
Add the bell peppers and sauté for 5 more minutes, until tender.
Add the celery and sauté for 5 more minutes, until translucent.
Add the tomatoes, stock, harissa, salt, bay leaves, and 4 cups water. Simmer for 25 to 30 minutes, until the vegetables are soft.
Stir in the chickpeas and simmer for 10 to 15 minutes, until soft. Add the parsley and lime juice and taste for seasoning. Keep warm over low heat.
Meanwhile, bring a large saucepan of salted water to a boil. Stir in the couscous and cook for 7 to 9 minutes, until tender. Drain and rinse with cold water to cool. Scoop ¼ cup of the couscous into each bowl and ladle the soup on top. Serve immediately.
