The smash burger taco is the rare sandwich whose defining move is a substitution at the bottom: the soft bun is gone, and a flour tortilla takes its place under the patty. A loose ball of ground beef is smashed directly onto the tortilla on a hot flat-top, so the meat sears and bonds to the dough instead of sitting on a separate slice of bread. That fusion is the whole idea. The tortilla is not wrapped around a finished filling the way it is in a taco; it is the cooking surface and the carrier at once, and the patty is welded to it before anything else goes on.
The craft is in the press and the order of operations. The beef is smashed thin against the griddle through the tortilla, which means the dough crisps and toasts where the fat renders into it, picking up a fried, blistered underside that a steamed bun never gets. American cheese goes on while the patty is still on the heat so it slumps into the seared crust and seals the meat to the tortilla rather than draping over the top. The build is finished cold and acidic on purpose: diced onion, sliced pickle, and a creamy pink sauce, which is the sharp, cool counter to a rich patty fused to a fried flatbread. The format folds in the hand the way a taco does, but it eats like a smashed cheeseburger turned inside out, the crust on the bread side instead of around the meat.
The variations stay inside the tortilla-as-bun logic. A double stacks two smashed patties on one tortilla; a version that crisps shaved onion into the patty borrows the Oklahoma onion build's trick on a flatbread base; a folded quesadilla-leaning build griddles cheese onto the tortilla itself so the dough crisps on both faces. The wider family of folded flexible-bread sandwiches, the taco, the torta, the quesadilla, runs on the same idea of a complete meal on a pliable carrier, and each of those relatives deserves its own article rather than being crowded in here.