I once heard that okonomiyaki was created after the war when food was scarce. I don’t know if this is true but it seems correct. All you really needs is flour, water, eggs and cabbage. Oh, and whatever leftovers you happen to have, and presto – Okonomiyaki.
A link for Hiroshima okonomiyaki from Setsuko Yoshizuka at About.com:Japanese Food. I’ve never made this with the Yakisoba noodles added. It looks good.