Slice the onion thinly across the grain, then cut in half. Chop the cabbage roughly.
Peel the potato, and julienne to 4 cm long. Soak into a bowl of water.
Put the okonomiyaki flour, egg and water into another bowl and mix with a whisk until there are no lumps. Add the onion and cabbage and the tempura crumbs.
Mix so that the batter coats the vegetables well.
Heat vegetable oil in a frying pan. Pour in 1/2 of the Step 5 batter.
Set the heat to low-medium. Turn in the edges of the pancake to make it nice and round, and press the middle lightly to form an indentation. Cook for 3 minutes.
When the pancake is golden brown, top with 1/2 the drained potato and turn the pancake over. Cover with a lid, turn the heat down to low, and cook for 5 to 6 minutes.
When the pancake has puffed up nicely and the other side has also turned golden brown, turn it over one more time, cook for another 1-2 minutes and transfer to a plate. Cook the other pancakes in the same way.
Top the pancakes with diagonally sliced green onion and mayonnaise. Eat while dipping in mentsuyu noodle dipping sauce. It's also delicious sprinkled with some shichimi spice (optional).
Story Behind this Recipe
This is a recipe proposed by the president of the Japan Flour Cooking Association, Mana Kumagaya! It's an "Okonomiyaki made easily in a frying pan." If you make okonomiyaki in a frying pan instead of a griddle, the clean up is easy. You can use kabocha squash instead of the potato and it will be delicious as well.
Mix the added ingredients and batter together so as to incorporate lots of air in the batter. Cook this as soon as it's mixed up, before the vegetables start to exude moisture.