Is it somehow possible to test if a restaurant really serves vegan burgers?

So I ordered food from a restaurant which has vegan food options. At least they labeled it like that. It is also a big chain in Austria so I would love to think that if they label something as vegan, than it should be vegan. My girlfriend thinks that the burger is made with real meat because it looks and tastes like chicken. How can I know that something really is vegan?