Tzatziki (Τζατζίκι) is a cold yogurt-cucumber-garlic sauce, and in the context of this catalog it is the single piece that defines whether a gyros or souvlaki wrap works or fails. It is not a sandwich, and pretending otherwise would miss the point. It is thick strained Greek yogurt loosened with grated cucumber, sharpened with raw garlic, rounded with olive oil and salt, and finished with dill or mint. On the street it is the wet, cooling layer that ties seasoned meat, raw onion, tomato, and warm bread together. Without it the wrap is dry and one-note; with it done well, every bite has acid, fat, and a slow garlic burn.
Built in order: thick yogurt is the base, so it should be drained yogurt or proper Greek-style, never thin supermarket yogurt that weeps water. The cucumber is grated, then salted and squeezed hard, because cucumber is mostly water and unsqueezed cucumber turns the whole bowl into a puddle within an hour. Garlic goes in raw and minced or grated to a paste so it disperses evenly rather than ambushing one bite. Olive oil is whisked in for body and gloss, salt is adjusted last, and dill or mint is folded through at the end so it stays fresh rather than going grassy. Good tzatziki holds its shape on a spoon, tastes of garlic without being acrid, and clings to meat instead of running off the foil. Sloppy versions are watery, under-salted, taste only of plain yogurt, or have been blended smooth into something closer to a dip than a sauce with texture.
The sauce shifts by hand and by region. Dill-forward versions read cleaner and herbal; mint versions feel rounder and slightly sweet. Some cooks add a splash of vinegar or lemon for extra cut, others keep it pure yogurt and garlic. Garlic load is the biggest variable, ranging from a faint background note to a deliberate, eye-watering hit, and that single choice changes the character of every wrap it touches. As a mezze served with bread rather than inside it, tzatziki sits alongside dishes like tzatziki kai meze, which deserves its own article rather than being crowded in here. Inside the pita it stays in its proper role: the cold, sharp counterweight that makes hot grilled meat worth eating wrapped in bread.