1. Sift flour into a large bowl, and then add water and egg to mix. Stir constantly to keep lumps from forming.
2. Add all vegetable, carrot (optional), leek, zucchini and cabbage, all ingredients for the seasoning of batter gradually and mix together well.
3. In a large pan, heat 1 tbsp vegetable oil and cook some of sliced pork belly. Split the pork in 3 on the pan.
4. Spoon the okonomiyaki mixture on the pork and spread it into a round shape of about 1 to 1.5cm thickness. Well, it doesn't really need to be perfectly round (Optional : If you want, spread some cheese on it and put more pork belly slice). Fry over medium heat until the bottom side becomes golden brown, then turn it over with a spatula and press down on the okonomiyaki to compress. Fry it uncovered until the other side is browned.
5. Transfer the okonomiyaki to a plate, put sauce and mayonnaise (to your taste) on it.