Put the onion, leeks, garlic, peppers, zucchini and mushrooms in a large saucepan. Add the tomatoes, port, tomato paste and ketchup and mix well.
Rinse and drain the chickpeas and add to the pan. Cover, bring to a boil and simmer gently for 20-30 minutes, stirring occasionally, until the vegetables are cooked and tender but not overcooked. Remove the lid and increase the heat slightly for the last 10 minutes of the cooking time, to thicken the sauce, if you like.
Stir in the olives and herbs and season with salt and pepper. Serve immediately, garnished with chopped mixed herbs.