Gyros Hirino me Tzatziki (Γύρος με Τζατζίκι) is pork gyros with tzatziki, named for the sauce because the sauce is the essential element here, not an optional dressing. Tzatziki is strained yogurt cut with grated cucumber, garlic, olive oil, and usually a little vinegar or lemon. Its job in this sandwich is double: it is the cold, acidic, garlicky foil to warm fatty pork, and it is the lubricant that ties shaved meat, raw vegetables, and bread into one cohesive bite instead of three separate ones. Without it the sandwich is dry and one-note; with it done well, every component reads at once.
The sauce goes on early and low. After the pita is warmed, tzatziki is spread directly onto the bread before the hot pork lands, where it forms a barrier that stops grease soaking straight through and gives the meat something to grip. Good tzatziki is thick enough to hold a spoon line and sharply garlicky, with the cucumber squeezed dry first so it does not weep. Sloppy versions are thin and underseasoned, made from unstrained yogurt or watery cucumber, and they slide out the open end of the wrap leaving a pale, sour smear and a soggy seam. Quantity is its own discipline: enough to coat, not so much that it drowns the spice of the pork and pools in the paper.
Within this version the real variation is the tzatziki recipe itself, since shops guard the garlic-to-yogurt ratio and the choice of vinegar or lemon, and that range is wide enough to deserve its own article rather than being crowded in here. Some kitchens add a second smear over the meat as well as under it; others keep it strictly as a base layer so the pork crust stays audible. The mirror-image order, the same gyros built deliberately without the sauce for people who want the meat and spice unmediated, is a distinct thing with its own logic and deserves its own article rather than being crowded in here. Here the whole sandwich rides on one ingredient, so the test is narrow and unforgiving: the tzatziki must be thick, cold, and properly garlicky, or the version named after it has no reason to exist.