Heat the olive oil in a large enameled soup pot over moderate heat. Add the zucchini, celery, and garlic; salt lightly and stir to coat with the oil. Cover tightly and steam-saute the vegetables for 10 minutes. After 10 minutes, add the stock, 1 teaspoon salt, herbs, carrot, and rice and season with pepper. Increase the heat and bring the soup to a boil. Reduce the heat to low, cover tightly, and simmer soup for 10 minutes without disturbing. Chop the spinach coarsely. After 10 minutes, stir the spinach and tomatoes into the soup. Cover tightly and simmer for 12 minutes without disturbing. Serve hot, passing the cheese at the table. Makes 6 to 7 servings.