Heat olive oil and butter in a large saucepan or Dutch oven over medium to high heat (note 1)
Add the onions, carrot and celery and cook for 5 minutes, or until onion is soft.
Next, add the green beans and zucchini and cook further 2 minutes.
Finally, add the potatoes and give a good stir.
Crumble stock cubes over the vegetables, then add the water and tins of tomatoes.
Stir well, season with salt and pepper.
Bring to the boil, reduce heat and simmer for 1 hour, or until vegetables are cooked and soup is thick. (note 2)
Serve with grated parmesan, extra salt and pepper and toast or fresh bread and butter.