Cut the onion, carrot, celery, tomato, and other vegetables into bite-sized pieces.
Heat olive oil in a pot and sauté the onions first.
Add carrots, celery, and tomatoes, and continue to sauté for another 2-3 minutes.
Pour in water or vegetable broth and bring to a boil.
Season with bay leaves, salt, and pepper.
Simmer for 20-30 minutes until the vegetables are tender.
Ladle the finished soup into bowls.