In a medium mixing bowl, whisk together flour, egg, and water (or dashi) until smooth.
Add shredded cabbage and chicken, stirring to coat evenly. The batter should be thick, with cabbage packed in rather than soupy.
Place a nonstick skillet or griddle over medium heat. Add 1 tablespoon of vegetable oil and swirl to coat evenly.
Once the oil shimmers, spoon the batter into the skillet and shape into a round pancake about 6 inches wide and ¾-inch thick.
Let the pancake cook undisturbed for 4–5 minutes, until the bottom is golden brown and crisp.
Use a wide spatula to gently lift the edge — it should hold together before flipping.
Carefully flip the pancake using a spatula (or two if needed).
Add another small drizzle of oil around the edges if the pan looks dry.
Cook for another 4–5 minutes on the second side until cooked through and firm in the center.
Transfer the pancake to a serving plate. Brush the top generously with okonomiyaki sauce.
Drizzle mayonnaise in a zig-zag pattern across the surface.
Sprinkle bonito flakes on top — they will curl and “dance” from the steam, adding flair to the presentation.
Add optional toppings like pickled ginger, green onion, or seaweed flakes for extra color and flavor.
Cut into wedges (like a pizza) and serve hot, straight from the skillet to the table.