Heat oil in a large stock pot over medium-high heat. Saute onion, carrot, and celery until onion is translucent and vegetables are tender, 5 to 7 minutes. Stir in tomatoes and Italian seasoning, and cook 5 minutes more, stirring frequently.
Dissolve bouillon cubes in water, and stir into vegetables. Adjust heat to a medium simmer, and cook approximately 10 minutes. Add zucchini and cabbage, sprinkle with garlic salt, and cook until tender, 5 minutes more. Adjust seasoning with salt and pepper, and serve.
