Souvlatzidiko (Σουβλατζίδικο) is not a sandwich but the place that makes them: the souvlaki shop, the establishment type that grills the skewers, turns the gyros cone, warms the pita and hands the result across a counter. The name is built from souvla, the skewer, and the -adiko ending that marks a shop dedicated to a thing. It is a fixed Greek institution, and understanding the format explains why the food that comes out of it tastes the way it does, because the building, the line and the equipment shape every wrap and skewer served.
The layout is functional and consistent enough to describe. At the front, a charcoal or gas grill running skewers in rows, and beside it a vertical rotisserie spit turning a stacked cone of seasoned meat under its own heating element. A flat-top or oven keeps pita moving, and a cold station holds tzatziki, sliced tomato, onion and salad within arm's reach of the person assembling. Fries come out of a fryer in a steady rotation. The work is sequential and fast: meat to the fire, bread to the heat, fillings laid in order, the wrap folded and twisted into paper, the whole exchange measured in the time it takes to make change. A well-run souvlatzidiko shows in the output, meat finished to order rather than pulled from a holding tray, pita warmed at the moment of assembly, fries fresh enough to still be crisp when they hit the wrap. A poorly run one shows just as plainly, skewers cooked ahead and held until dry, bread reheated stiff, a cone left turning past its prime so the shavings go from crisp-edged to greasy and tired.
The dishes that come out of this place each stand on their own. The skewered kalamaki, the wrapped pita, the cone-shaved gyros and the mixed-meat skewer are distinct foods and deserve their own articles rather than being crowded in here. What the souvlatzidiko entry exists to capture is the format itself, the grill-and-spit shop that is the common origin point for all of them, and the simple operational truth that defines a good one: nothing held warm, everything finished to order, assembled at the counter the moment it is ordered.