In a large pot, heat the olive oil over medium heat. Add the chopped onion and garlic. Sauté for about 3-4 minutes until the onion becomes translucent.
Add the chopped carrots and celery to the pot. Cook for an additional 5 minutes, stirring occasionally, until they start to soften.
Stir in the chopped cabbage, and cook for another 5 minutes, allowing it to wilt slightly.
Pour in the vegetable (or chicken) broth and add the diced tomatoes with their juice.
Season the mixture with dried thyme, salt, black pepper, and the bay leaf. Bring the soup to a boil.
Once boiling, reduce the heat and let simmer for 25-30 minutes, or until the vegetables are tender.
Taste the soup and adjust the seasoning if necessary. Remove the bay leaf before serving.
Serve the soup hot, garnished with fresh parsley if desired.