What turns chili and cheese into a burger? The bun. Carne asada into a taco? The tortilla. Grilled PB&J into a sandwich . . . well, you get it. It seems that every civilization on Earth has figured out that the best way to eat food is with your hands, using some form of bread as the vehicle from plate to mouth. In Sam Zien's hands, every burger, taco, tortilla, and sandwich is as cheesy, toasty, dripping-with-good-stuff as possible. Between the...