This is a kind of teppanyaki (food grilled on a hot plate), and is a homey favorite among the Japanese populace. It is a specialty of Osaka and Hiroshima.
Okonomiyaki is made with wheat flour and water mixed with vegetables such as cut cabbage. It is common to order toppings such as meat and seafood and then season it with a savory sauce and mayonnaise. The method of baking and ingredients differ from region to region.
Kansai style features a thick batter with cabbage mixed in. Hiroshima style often has Chinese noodles mixed in.
Also popular in Osaka is negiyaki, which uses green spring onions instead of cabbage. Baked thinner than okonomiyaki, it is seasoned with lemon soy sauce or pepper powder, and is very healthy.