Actually, its name says all: konomi can be translated as "what you like" and yaki means "grilled". So, besides the pancake - which is made with flour, grated nagaimo (a variety of yam), water or dashi and eggs - Okonomiyaki can be prepared with cabbage, vegetables, pickled ginger, green onion, meat (usually pork or bacon), shrimps, clams, scallops, squid, oysters, octopus...
You can find Okonomiyaki in restaurants (where the ingredients can be provided separately, so you can prepare your own version) or you can taste it at festival stalls... and although it doesn't look as fancy as other Japanese dishes, Okonomiyaki is delicious and I strongly recommend you to try it...
EXIF info:
Nikon D90
Lens: 8-16mm F/4.5-5.6G
Focal Length: 16mm
Aperture: F/5.6
Shutter Speed: 1/60s
ISO Sensitivity: ISO 640