In a large pot over medium heat, add the Italian beef sausage. Break it apart with a spoon and cook until browned, about 5-7 minutes. Remove excess grease if needed.

Add chopped onion and garlic into the pot and sauté for another 3-4 minutes until they are fragrant and translucent.

Stir in the diced zucchinis and diced tomatoes, allowing the mixture to cook for an additional 3 minutes.

Add the vegetable broth and Italian seasoning, bringing the entire pot to a boil. Then, reduce heat to a simmer.

Season with salt and pepper to taste. Let it simmer for about 15-20 minutes or until the zucchini is tender.

Ladle the soup into bowls and top with fresh basil and grated Parmesan if desired.