In a large soup pot, sauté the onion and garlic until translucent and fragrant. Add canned tomatoes and stir. Cook for five to 10 minutes to let the tomatoes break down a bit. Add the diced zucchini and broth, then add the oregano, basil, salt, and pepper.

Cover and cook for about 20 minutes until the zucchini has softened but still holds its shape. Add the sugar and the vinegar, if using. Mix well and cook for five more minutes.