For the batter, mix flour, chicken powder, baking powder, and salt&pepper. Add water and whisk to combine. Incorporate the egg. Add cabbage and green onion (and any other additions – ham, dried shrimp, etc).
Pour into a hot pan with oil, shape into a round pancake. Cover and let cook for a few minutes until the bottom is golden brown. Flip, and finish cooking.
Mix all sauce ingredients together. Brush atop the pancake, drizzle with Japanese mayonnaise, and top with bonito flakes (if available).