This can be romanized a few ways: moui or mo-i, I think are most common. Moui known in English as Chinese cucumber, red gourd, or just yellow cucumber. It is a pretty common summer vegetable here in Okinawa, and since it is getting cheap in the markets, I will probably make some pickles from it.
It pretty much tastes and looks like a large yellow cucumber. It can be eaten plain, pickled, or even cooked in soups.
Click for a recipe on this page.