Cook ravioli or tortellini according to package directions.
Meanwhile, in a medium saucepan combine stewed tomatoes, undrained clams, zucchini, and Italian seasoning. Bring to boiling; reduce heat. Simmer, uncovered, for 1 minute. Stir together the tomato sauce and cornstarch until well blended; stir into hot mixture. Cook and stir over medium heat until thickened and bubbly. Cook and stir for 2 minutes more. Serve clam sauce over hot pasta. Sprinkle Parmesan cheese over each serving. Makes 3 servings.