Somewhere you can just sit down and order.
Athens is full of tavernas, and almost none of them are for you. That's exactly why King David Burger exists, the first burger in the city where someone who keeps kosher can just sit down and order, no questions asked. The beef sears over the flame until the edges catch, lands in a soft sesame bun, and carries far enough to reach you from the street. All of it Mehadrin-certified under Tiferet Yisrael. At Ermou 78, right on the route up to the Acropolis. Stop in on the way, leave full.