Let's wade in, shall we?
A common definition isn't always the technical definition. A sandwiches is basically two pieces of bread with filling, generally handheld. This quickly falls apart with open faced sandwiches and sandwiches with messy filling that are best eaten with a fork. Of course, some messy sandwiches, such as BBQ or Sloppy Joe's are often eaten out of hand. There are also finger sandwiches that are often stacked and cut so there are more than two slices of bread. This area becomes confused when you get to hamburgers and hot dogs. Are they sandwiches? Sure! And tomatoes and cucumbers are fruits, commonly referred to as vegatables.
What we have so far is leavening. When you get to tortillas you have flat bread. Ok, let's say a quesadillas is a sandwich, and many, such as
@vapeanderson, fold the tortilla, and many, such as the OP, add more than cheese. What if you use a corn tortilla, instead of flour? You get a taco. Is that a sandwich? How about we go back to the flour tortilla, and we add a few more folds. Now you have a burrito. Is that a sandwich? What if you pour sauce on it, and bake it? Is an enchilada a sandwich? Or going back to sliced, leavened bread, is French toast topped with fruit or a filling a sandwich? What about a Monte Cristo? A croque monsieur?
Is leavening the defining feature? If a quesadilla is a sandwich, are stacked cheese and crackers a sandwich? What if you roll the quesadilla? Is a lavash a sandwich? If not, why not, when you can make spiral finger sandwiches?
What if you don't use bread? Say you use cake. Is cake disqualified because it's sweet? We know filling can be sweet because of jams and jellies. You can make a sandwich out of cinnamon bread, and it's sweet. When does bread become cake, and get disqualified? What about quick bread? Banana bread? Zucchini bread? And if we say cake is as close as a cracker, or tortilla, then what if we fill and roll it like a lavash? Is a jelly roll a sandwich?
When I first saw this thread, I asked Madri-Guy, the graduate of a fine culinary academy, what he thought. He said, "when you start getting into definitions about food, you end up in arguments where cold cereal in milk is a soup."
Wise words, Madri-Guy.
@ThymeTraveler, what do you think?