In 10-inch skillet cook zucchini, celery, and onion in butter or margarine till tender.
Add chicken livers; cook about 5 minutes or till just browned.
Stir in the 3/4 cup water, the skim milk, bouillon granules, tarragon, salt, and pepper.
Cover and simmer 5 minutes.
Combine cornstarch and the 1 tablespoon cold water; stir into liver mixture.
Cook and stir till mixture is thickened and bubbly.
Cook and stir 1 to 2 minutes more.