Clean and slice vegetables such as onion, carrot, celery, and bell pepper.
Heat olive oil in a pot and sauté the onion and garlic.
Add all the remaining vegetables and stir-fry over medium heat.
Add tomatoes (or tomato sauce) and mix well.
Pour in vegetable broth and bring to a boil.
Season with salt and pepper, then simmer over low heat for 30-40 minutes.