Taco meat is a type of meat, it's not the same as delicious meat (which just tells you additional information about the meat).
So basically, just consider taco meat to be the same thing as mobile phone or profile picture (almost a single word), and the comma is needed only if you are using more than one adjective that gives you a characteristic of the thing you are talking about (for example "a cheap, powerful device" or "a brave, admirable man")
"They serve cheap and delicious meat." is correct.
Hope this clears it up for you!