Combine all-purpose flour and salt in a large bowl. Pour in 1¼ cups (300ml) water. Gently mix until just combine.
Preheat a large non-stick electric griddle (or large non-stick pan on the stove) on medium heat. Brush griddle with a little oil. Spread a ladle of the batter into a thin 8 inch round on one side of the griddle. Sprinkle a teaspoon of katsuobushi on the top.
Place a handful of shredded cabbage on the pancake and 4 half slices of bacon on the cabbage. Allow pancake batter to set, about 5 minutes.
Flip pancake over using 2 spatulas so that the bacon is now touching the griddle. Continue to cook for 4 to 5 minutes.
In the meantime, cook a portion of yakisoba on the side (or in another pan) with 1 tablespoon mirin and 1 tablespoon okonomiyaki sauce.
Cook 5 to 6 shrimps next the noodles. When shrimps curl and turn pink, transfer onto the fried noodles.
Now, move the pancake onto the noodles.
Crack an egg onto the side of the griddle and spread it out into an 8 inch round. Move the entire pancake (with noodles) onto the egg. Allow it to cook for another 1 to 2 minutes.
Flip the completed okonomiyaki over. Drizzle or spread a generous amount of okonomiyaki sauce on the top.
Transfer to a plate. Sprinkle with aonori (finely shredded green seaweed) and green onions.