Cut onion, cabbage, carrot, and bell pepper into bite-sized pieces.
Pour olive oil into a pot and sauté the onion.
Add cabbage, carrot, and bell pepper and stir-fry for another 2 minutes.
Add water and canned tomatoes and bring to a boil.
Season with bay leaf, salt, and pepper.
Simmer over medium-low heat for 20 minutes until the vegetables are cooked through.