Cucumber

From Memory Alpha, the free Star Trek reference

A cucumber is a vegetable native to Earth used as food. It is the main ingredient in cucumber sandwiches. (VOY: "Persistence of Vision")

Something similar in appearance to cucumbers grew on vines on Hanon IV. In 2373, the crew of the USS Voyager was able to use the foodstuff as sustenance when stranded on the planet. (VOY: "Basics, Part II")