Combine 10 cups water, onion, and the next 4 ingredients (10 cups water through bay leaf) in a large Dutch oven; bring to a boil. Cover, reduce heat, and simmer 30 minutes. Remove 2 cups cooking liquid; set aside. Add squash and next 6 ingredients (squash through chickpeas) to onion mixture. Simmer 25 minutes or until squash is tender. Stir in chard, cilantro, 2 teaspoons salt, and black pepper; cook 5 minutes or until chard wilts. Stir in juice. Discard bay leaf.
Place couscous in a large bowl. Combine reserved cooking liquid and remaining 1 1/2 cups water in a small saucepan; bring to a boil. Stir in remaining 1/2 teaspoon salt and oil. Pour water mixture over couscous; stir well to combine. Cover and let stand 20 minutes or until liquid is absorbed. Fluff with a fork. Serve vegetable mixture over couscous. Top with crumbled cheese.
Prepare the couscous as the vegetable mixture simmers. Try serving with harissa, a Tunisian hot sauce found in Middle Eastern markets and large grocery stores.