To a saute pan on medium-low heat, add olive oil. When olive oil is heated, add chopped red onion and saute until beginning to turn translucent. Add garlic, carrot, celery, and zucchini. Cook until onions are translucent and the garlic is starting to brown (about 8 minutes).
Add cabbage, stir, and cook covered for 5 minutes.
Add diced tomatoes, thyme, white vinegar, salt, pepper, and stock, and again thoroughly stir the mixture. Bring it to a low boil.
Then, reduce the heat to a gentle simmer. Simmer the soup, uncovered, for 20-30 minutes, stirring occasionally, until the cabbage is tender.
Add additional salt and pepper to taste and serve.