A mushroom was the fruiting body of certain fungi. Many varieties were edible and used in assorted culinary dishes.
In 1986, Doctor Gillian Taylor ordered a mushroom and pepperoni with extra onions pizza at an Italian restaurant. (Star Trek IV: The Voyage Home)
Mushroom soup was one of Chakotay's favorite foods. In 2371, Seska found some mushrooms on a planet in the Delta Quadrant, and made it for him. (VOY: "State of Flux")
Tom Paris suggested grilled mushrooms to Harry Kim as a first meal after being rescued from an Akritirian prison in 2373. (VOY: "The Chute")
When Worf and Jadzia Dax briefly called off their wedding in 2374, Julian Bashir took the opportunity to break from Kal'Hyah and order a steak with mushrooms, a baked potato, sour cream, and chives. (DS9: "You Are Cordially Invited")