The premise is simple: one of these things is not like the other. Sometimes the themes are based on vocab / idioms ("A to Z", "Soup to Nuts", "The Works") other times idiosyncratic knowledge (Sloppy Joe, French Dip, Tuna Melt).
The fun lies in connecting the two. In this example, "Full Monty" is another idiom that means "Everything", but sounds like it could be a sandwich.
Eager to hear what you think!