Put cabbage, spring onion, egg, soy sauce, flour and water in a bowl and mix well to combine.
Heat a frypan over a low to medium heat and add a splash of oil for frying.
Tip the okonomiyaki mixture into the pan and use a spatula to form it into a round pancake about 2cm thick. Take your time cooking it - it's thick and you don't want raw mixture in the middle. When golden brown on the bottom, carefully flip and cook the other side until golden too. It's not essential, but I find it helpful to put a lid on the frypan for some of the cooking time to help it cook through.
Remove from the pan and serve immediately, or keep warm in a low oven while you cook more pancakes.
Top with your choice of condiments, slice into wedges and enjoy!