Update: Want to make okonomiyaki from scratch? Try this detailed recipe! 
UK and European residents only: Japan Centre  in London is having a sale this week (until May 14th) on okonomiyaki ingredients: Nissin pre-mixed okonomiyaki flour , okonomiyaki sauce , and the all-important Kewpie mayonnaise .
Okonomiyaki is often described as a Japanese pizza, but it’s more like a savory thick pancake with lots of added ingredients. You can make it from scratch of course, but it is a bit fiddly, so the mix, which includes things like dried shrimp and tempura batter bits (tenkasu), makes it much more convenient. Just add your own additives like shredded cabbage, bean sprouts, thin slices of pork or even bacon, beni sho-ga (red dyed pickled ginger), and so on. The classic okonomiyaki sauce is made by mixing a sweet, barbeque sauce-type sauce with mayonnaise right on top of the hot okonomiyaki, though I also like it just with a dribble of plain soy sauce or a soy-ginger sauce.
The description on the Japan Centre page is a bit wrong though - it’s not a Kyoto delicacy by any means, it’s an Osaka delicacy. Kyoto people would regard okonomiyaki as being rather common!
[Edit: it’s been corrected  now. (Thanks Simon!) Hiroshima style okonomiyaki incidentally is the Chicago Deep Dish Pizza version of okonomiyaki, loaded up with ingredients like stir-fried yakisoba noodles, seafood, etc.]
(Disclaimer: Japan Centre is a Just Hungry advertiser, but I’m also a satisfied mailorder customer. See if they deliver to your country .)