Place olive oil in heavy large saucepan over medium heat. Add onions and carrots; sauté until vegetables are tender but not brown, about 8 minutes. Add stock and bring to boil. Add fava beans and green beans and simmer until almost tender, about 8 minutes. Add asparagus and fresh basil and simmer until all vegetables are very tender, about 7 minutes longer. Season the soup with salt and pepper. Ladle soup into bowls. Sprinkle with fresh Parmesan cheese if desired. Serves 4.