Heat the oil in a large soup pot. Add the onions and saute over moderate heat until golden. Add the potatoes, pumpkin or squash, carrots, tomatoes, and enough water to cover. Bring to a boil, then add the seasonings and simmer over low heat, covered, for approximately 45 minutes, or until the vegetables are tender.
Add the chick peas and season to taste with salt and pepper. Simmer over very low heat for another 15 minutes.
In the meantime, place the couscous in an oven-proof bowl. Cover with two cups of boiling water, then cover the bowl and let stand for 15 minutes. Fluff with a fork. Place a small amount of the couscous in each soup bowl, then ladle the soup over it. Serve at once.