Preheat the oven to 210C fan / 430F. In a large bowl, combine the flour, baking powder, sugar, and salt with a whisk. Then, add in the eggs followed by the chicken stock. Whisk until a smooth thick-ish batter has formed.
Next up, add your chopped cabbage, sliced onion, minced garlic, and grated cheese into the bowl. Mix with a spatula until the ingredients are fully coated and well combined. You want the batter to be chunky and reasonably thick...not at all runny.
Get your tray and drizzle with sesame oil. Place in the oven for 3 minutes until hot. Remove from the oven and transfer the batter into the tray and evenly spread it and flatten the okomiyaki batter. Top with the streaky bacon evenly and place in the oven for 20 minutes.
Once the bacon is cooked and slightly crispy around the edges, remove from the oven and top with the brown sauce (spread it all over the okonomiyaki), then drizzle over the mayonnaise, sprinkle with spring onions, sesame seeds, and then serve up and enjoy!