Cut onion, tomato, cabbage, celery, and carrot into bite-sized pieces.
Add olive oil to a pot and sauté the onion.
Add cabbage, celery, and carrot and continue to sauté together.
Add tomato and sauté for 2 more minutes.
Pour in water and bring to a boil.
Season with salt and pepper, then simmer over medium heat for 20 minutes.