Heat olive oil in a large pot over medium heat.
Add chopped onion and garlic; sauté until soft and fragrant, about 5 minutes.
Add carrots, celery, zucchini, green beans, and potato; stir and cook for 5 minutes.
Pour in vegetable broth and add dried thyme.
Bring to a boil, then reduce heat and simmer for 20 minutes, or until vegetables are tender.
Use an immersion blender to blend the soup until smooth and creamy.
Stir in heavy cream if desired, and season with salt and pepper.
Serve hot, garnished with fresh parsley.