Can't go past okonomiyaki - simple to make if you're not in your own kitchen, provided you've got the right ingredients. Especially the "sauce" sauce and japanese mayonaise.
From what I've seen (and it might just be because the girls who cook for me aren't very traditional) a lot of japanese cooking comes from packet-mixes - just add water. Gurutan, curry (which I've always made from frying curry powder), monja, miso soup, etc. This means that you can get a couple of courses together with minimum effort.
I have a question, too. When I'm cooking for girls I like to do something like a flaming creme brulee - something with a little excitement. Is there anything exciting like this in Japanese cooking?