Run the raw vegetable sandwich over a fire and the grill changes everything: this is the cooked answer to it. Zucchini, eggplant, and pepper are sliced, cooked over heat until they soften and char at the edges, dressed with olive oil, and laid cold or barely warm into split bread. It reaches southern France, where these are the everyday summer vegetables and olive oil is the default fat. The char is not incidental; it is the flavor the sandwich is built around.
The craft turns on what grilling does to water. Raw zucchini and eggplant are mostly moisture and would soak the bread; cooked, they lose that water and concentrate, picking up a smoky bitterness at the burnt edges that the olive oil then carries through the whole sandwich. That oil is the binder, so the bread needs a firm crust to hold it without going slack, and the vegetables are layered rather than packed so each keeps its own char. Like other oil-rich builds, it improves slightly as it sits and the bread absorbs what the vegetables give up. It is eaten cold or just warm, never hot, and it survives a few hours better than the raw version because the work is already done.
Variations stay in the southern vegetable register. A round of fresh goat cheese cuts the oil with a little tang; a few olives or a smear of tapenade deepen the salt; the cold ratatouille version packs the same vegetables stewed soft rather than grilled. The Sandwich aux Légumes Grillés belongs with the plant-forward builds the catalog groups under Sandwich Végétarien. Its specific contribution is the char: a vegetable sandwich whose flavor comes from the grill and the oil, not from the produce being raw.