In a large pot or Dutch oven, heat the olive oil over medium heat.
Add the Italian sausage to the pot, breaking it up with a spoon as it cooks. Sauté until browned and cooked through, about 5-7 minutes.
Add the diced onion to the pot and sauté for 3-4 minutes until it becomes translucent.
Stir in the minced garlic and cook for an additional minute until fragrant.
Add the diced zucchinis, canned diced tomatoes (with their juice), chicken or vegetable broth, dried oregano, and dried basil. Stir to combine.
Bring the soup to a boil, then reduce the heat to a simmer. Cover and let it cook for about 20-25 minutes, or until the zucchinis are tender.
Season with salt and pepper to taste.
Serve hot, garnished with fresh basil leaves and grated Parmesan cheese if desired.