Roasting the onions, garlic, capsicums, potatoes and zucchini caramelises their natural sugars to bring out tantalising sweetness. The pan juices, which contain minimal fat, are added to the soup so you won't lose a drop of flavour.
By using deeply coloured vegetable ingredients like carrot juice and fresh or canned tomatoes as the basis for soups, you'll be getting a wide spectrum of nutrients and far less fat and sodium than from purchased chicken stock. And you'll also benefit from a number of potent, disease-fighting carotenoids, such as beta carotene and lycopene.