A sandwhich is wholly and unarguably, by definition, two pieces of bread with any sort of ingredients between them. Temperature and content of ingredients is irrelevant. You wanna put an old boot between two slices of bread? You got yourself an old boot sandwhich.
Throw in some ketchup? Ketchup boot sandwhich.
Main point is-- it's a sandwhich. A hamburger is a sandwhich. A hotdog is not a sandwhich, and neither is a taco-- but a hamburger is undeniably a sandwhich.
Source: Worked in a deli for 4 years, am sandwhich expert.
PS: Hotdogs are counted as sandwhiches strictly by New York Tax laws. I disagree.