Heat oil in a heavy-bottomed saucepan over medium-high heat. Add celery, onion and thyme; sauté until vegetables are soft, about 5 minutes. Add garlic and sauté until fragrant, about 30 seconds.
Add zucchini, green beans, salt and pepper; sauté until slightly soft, about 2 minutes Add stock and tomato; increase heat to high and bring to a boil. Reduce heat to low, cover and simmer 10 minutes. Stir in parsley. Serve hot.