Whisk together egg and dashi. Add flour, baking powder, salt, pepper and whisk until combined. Fold in vegetables gently, coating.
In a large skillet over medium heat, heat 2 tbsp of oil. Scoop half the batter into the skillet and spread evenly, about 1/4 inch thick. Cook until golden on the bottom, about 3 minutes.
Lay half the pork bely evenly over the top. Flip and lower heat to medium-low. Do not press! Cook until browned, about 3 minutes. Transfer to a large plate, then repeat with remaining batter.
Whisk together all the ingredients for the sauce.
Drizzle okonomiyaki with sauce and kewpie. Sprinkle with toppings: green onion, nori flakes, bonito flakes, and pickled ginger. Serve hot.