Okonomiyaki is usually translated as a "pancake" though it's closer to an omelette than many things.
It is pretty much filled with whatever you like and then fried (the name itself translates to something along the lines of 'Cooked What-You-Like.") Usually it is then served with a sauce, like mayonnaise or soy sauce. It's a great way to use leftovers and odds and ends.
The batter recipe I use is made as so:
3 eggs, beaten
1/3 cup water
3 tbs flour
1/3 tsp salt
1/3 tsp baking powder
Beat all ingredients together to form an even batter.
Now, for the dish itself... basically, stir-fry any meat, noodles or veggies you want in a pan, and when they're cooked through, pour on the batter and let it fry till set. You should probably turn the pancake during the cooking process, though this can be a bit of a challenge... make sure your pan has been greased well.
Here are some photos of an okonomiyaki I made with spinach and peas, topped with sriracha sauce.