Most green olives can only season a sandwich; one is gentle enough to lead it. The Lucques is a green Languedoc table olive with a curved crescent shape, a bright grass-green color, firm flesh, and a mild, buttery, almost nutty taste with very little of the harsh brine bitterness that defines most green olives. That gentleness is the point: a Lucques is closer to a vegetable than to a condiment, which is why it can carry a sandwich rather than just season one. The bread is a good crusted loaf, and the build is the olive in volume, pitted and either left whole, chopped, or worked into a tapenade, set against the bread with very little else.
The mildness shapes everything downstream. A sharp brined olive can only ever be an accent, a few slices fighting for attention; a Lucques is soft and buttery enough to be present in quantity without turning the sandwich aggressive, so it can sit as the main savory element rather than a garnish. That is the design logic: lean on the olive's own fat and gentle flavor, and keep accompaniments quiet so they do not overwrite it. A whole-olive build wants good bread and perhaps a film of butter or fresh cheese to bind the loose olives so they do not roll out at the first bite. A tapenade build spreads the same olive across the crumb and behaves more like a seasoned paste, the bread carrying it the way it carries any spread. Either way the loaf needs a real crust, since the filling brings no body, and the restraint is deliberate, since a stronger element would bury the very thing the sandwich is named for.
Variations are about form more than substance. Whole pitted olives against bread is the plainest; a Lucques tapenade with a little oil and perhaps anchovy is the more concentrated; a fresh white cheese alongside softens and stretches it. The frame stays put: the Languedoc olive as the lead, the bread restrained around it. The Sandwich à la Lucques belongs with the place-named French sandwiches the catalog groups under Regional Specialty Sandwiches, the broad shelf of sandwiches tied to a particular corner of the country. Its specific contribution is an olive mild enough to be the sandwich rather than season it.