Primary ingredient of Salisbury "Steak" is toast..... THAT'S what is on the label for the Encore Salisbury Steak family pack....go read it in your local grocer's freezer section.
My grandmother made the best little hamburger steaks, onions and gravy when I was growing up. It was true "comfort" food. I have made Salisbury steak a number of times. Always taste great, but it still is not as good as grandma. Shalom
Don't buy the frozen crap, Salisbury steaks are quick & easy to make at home, there's many recipe variations on the web so folks can personalize to their taste!
All Salisbury steak recipes have to have 2 TBSP of prepared horseradish in them, or they don't have that signature flavor. Anything else is just plain old hamburger steak.