Cut onion, carrot, celery, tomato, and cabbage into bite-sized pieces.
Add olive oil to a pot and sauté the onions.
Add carrot, celery, and cabbage and stir-fry for another 2-3 minutes.
Add tomato and water, then bring to a boil.
Season with bay leaf, salt, and pepper, and simmer on low heat for 20 minutes.
Serve the finished soup in a bowl.