Cut onion, carrot, celery, and cabbage into bite-sized pieces.
Heat olive oil in a pot and sauté the onion until it becomes sweet.
Add carrot, celery, and cabbage, and stir-fry together for 2-3 minutes.
Pour in water or vegetable stock and bring to a boil.
Add tomatoes and simmer over medium-low heat for 20-30 minutes.
Season with salt and pepper to taste.