The Sandwich Grec is the late-night street staple, and the name is the least accurate thing about it. It is a French take on the döner kebab: spit-roasted meat shaved thin, packed into a folded flatbread or a split galette, dressed with salad and a white garlic sauce, and, the move that makes it French, a layer of frites loaded inside the sandwich rather than served beside it. What defines it is that last detail. The chips go in, soak up the meat juices and the sauce, and the sandwich becomes a full hot meal you can eat walking, which is precisely what it is for.
The logic is fast-food architecture working at the lunch and late-night peaks. The flatbread is warmed so it folds without cracking and holds heat around the filling; the meat is shaved off the vertical spit in thin sheets so it stays tender and packs evenly; the sauce blanche, a cool garlic-mayonnaise, ties the hot meat and the hot chips together and keeps the whole thing from drying out. The frites inside are structural as much as flavor: they bulk the sandwich, soak the juices that would otherwise make the bread soggy, and turn it from a snack into a meal. It does not survive sitting, it is built to be handed over hot and eaten immediately, and within a few minutes of the counter is when it is at its peak. The cook's job here is steady volume at the rush, not refinement.
Variations are mostly meat and heat. Lamb at the top end, veal or chicken as the standard, the choice changing how rich it reads; the sauce swapped or doubled, sauce blanche giving way to harissa or samouraï for heat; the flatbread traded for a galette fold or a split half-baguette for a firmer hold. Each is a recognizable adjustment of the same shaved-meat-and-chips idea. It belongs with the spit-roasted street sandwiches the catalog groups under Sandwich Grec / Kebab, and its specific contribution is the chips folded inside, the detail that turned an imported kebab into a French street meal.