It is no more "worthy" of being called a burger than a chicken or fish sandwich. Below is the definition of a hamburger to help clear the confusion for you.
A hot sandwich consisting of a patty of cooked ground beef, or a meat substitute, in a sliced bun, sometimes also containing salad vegetables, condiments, or both; The patty used in such a sandwich; Ground beef, especially that intended to be made into hamburgers
en.wiktionary.org/wiki/hamburger
As you can see, GROUND beef is a requirement.