Chicken Tetrazzini has cheese in it. Chicken a la King does not. Both good versions start with a rue (butter/flour then cream) complimented with the magical trio of vegetables (onions/carrots/celery...unless you're in the Bayou where it's onions/gr peppers/celery) and herbs de province (typical herbs of bay leaves, thyme, sage, salt and pepper, etc). [For Tetrazzini you would add Parmesan cheese or shredded chedder.] Add peas, mushrooms and your pre-cooked cubed chicken or turkey and voila...you have it. (adding a little white wine is optional) . 1950s version...open a can of Campbell's cream of mushroom soup. Add a package of frozen peas and carrots and heat on stove. Add a can of sliced mushrooms, some pre-shredded cheese, your cubed left over turkey and voila...an abomination.