In a large soup pot or dutch oven, heat the oil on medium heat. Meanwhile, peel and coarsely chop the onion, adding it to the pot as you chop. Add the garlic and cook, stirring occasionally, until tender, about 3 minutes. Add the mushrooms and cook until they begin to release thier liquid, about 2 minutes. Meanwhile open the cans of broth and tomatoes. Add the broth adntomatoes. Raise the heat to high. Cover the pot and bring the soup to a boil. Lift the lid briefly to add the Worcestershire and basil. When the broth comes to a rolling boil, add the tortellini. When the broth comes back to a boil, continue to cook for 3 to 4 minutes, or just until the pasta is tender. Serve at once, passing Parmesan cheese at the table to sprinkle on top, if desired. Serves 6, about 1 1/2 cups per serving. 202 cal., 6 grams fat(trace sat), 29 grams carb., 8 grams pro., 676mg sodium, 12 mg cholesterol, 27mg calcium, 2 grams fiber