It comes from an episode of Bleach where a running gag involving Orihime wanting to cook something very strange was used. While telling some friends about her cooking, she was twirling a leek (apparently part of the dish).
One version can be viewed at http://www.leekspin.com.
In the game Scribblenauts, there is a summonable item called "Loituma Girl". It is a person holding a leek. For some reason, she almost immediately disappears.