"What kind of meat do you have on your plate?"
Translation:Jaké máš na talíři maso?
váš - is a plural possesive in the sense that the owner is plural - vy. Then you can, of course, decline it for the object owned to be singular - váš, or plural - vaši, vaše.
But you are mixing máš, which relates to singular ty, and váš, which relates to plural vy. With ty máš you use the tvůj possesive.
Finally, it is much better to use the svůj possesive, when the object owned belongs to the subject of the sentence: "Jaké maso máš na svém talíři?"