Here's your answer...
Mongolian style lunch is servered different ways on different ships. Some ships have "Counter/Self service" in an area in the buffet. You grab a bowl, add protein, noodles and veggies, and give it to the chef. He adds sauce, woks it all together while you wait, and hands it back to you.
On ships that have Jiji's, you get served via a "fill in the box" menu, as Saint Greg stated above.
We usually make Jiji"s our "go to " spot for our embarkation lunch, as it is usually empty. Fellow cruisers don't realize that ther is a really good lunch there until later in the cruise.
Hope this helps...