Most participants in this debate are far too preoccupied with the shape or structure of the sandwich, to the point of neglecting what a sandwich is all about. It's simple. A sandwich is when you use bread as a handheld base for prepared foods that would otherwise be too messy to eat with your fingers. A tortilla is a flat bread, ergo handheld burritos and soft tacos are sandwiches.

"Then why isn't pizza an open-faced sandwich?" Because pizza has a crust, not bread. When you take raw dough and bake it along with its toppings or fillings, it may be a pie or a pastry or a pizza or a casserole or some other category I don't care to quibble over. It's not a sandwich.

Obviously there are many sub-categories of sandwiches. A dish isn't necessarily excluded from being a sandwich just because it's also another type of food.