Heat olive oil in large casserole over medium-high heat, add onion, celery, carrot and cook until very soft, about 7 minutes
Stir in the potatoes, parsley and basil and cook about 2 minutes, Add the tomatoes and 3 cups (half) of the stock, bring to a boil and reduce heat to medium. Simmer to warm through and cook the potatoes
Add in the Zucchini and the rest of the stock, season with salt and pepper. Cover and return to a boil. Simmer for about 10 minutes.