You can simmer almost any soft, filled pasta in chicken soup, from Lighter, Steamed Wontons (page 33) to ravioli (page 156). Tortellini, which can be bought in any supermarket, is my favorite. Use less pasta if you want a light soup, more if you want this as a main course.
Place the stock in a large, deep saucepan or casserole and turn the heat to medium‐high. When it is just about boiling, turn the heat to medium‐low and add the carrots and the onion. Simmer until the carrots are just about tender, 10 to 20 minutes depending on the thickness of the slices. Taste and add salt and pepper. Meanwhile, bring a pot of water to boil for the pasta.
Add the watercress or spinach to the simmering broth. Meanwhile, cook the tortellini until nearly tender. Drain it and add it to the soup.
Check and correct seasoning if necessary, spoon into bowls, and pass the Parmesan at the table.