Heat oil in a large stock pot over medium-high heat. Add onion, carrots, and celery; cook until onion is translucent and vegetables are tender, 5 to 7 minutes. Stir in tomatoes and Italian seasoning; cook 5 minutes, stirring frequently.
Dissolve bouillon cubes in water in a large glass, heat-proof, measuring cup; stir into vegetables in the pot. Reduce heat to a medium simmer; cook about 10 minutes. Add zucchini, cabbage, and garlic salt; cook until tender, about 5 minutes. Season with salt and black pepper. Top servings with Parmesan cheese.
