In 1985, Rodolfo Neri Vela, a Mexican scientist, served on a mission of the space shuttle Discovery. He brought tortillas. These proved to be an incredibly practical food in zero gravity. NASA astronauts have been using them ever since when attempting to make sandwiches.
That doesn't mean the results are always pretty. Pictured above is a cheeseburger made by astronaut Terry W. Virts, who is currently on board the International Space Station. The burger consists of broken up beef patty, cheese paste, tomato paste, and Russian mustard on a tortilla. He describes it as "VERY TASTY!"
-via First We Feast