How to Make It
Heat an 8-inch Belgian waffle iron. Add the bacon, close the top and cook on medium-high until browned and crisp, about 5 minutes. Drain on paper towels.
In a medium bowl, beat the eggs with the stock, butter, flour and salt. Scatter the cabbage, carrot and 1/4 cup of scallions on the waffle iron and cook on high, without closing, until sizzling, about 30 seconds. Gradually pour the egg mixture on top and cook, without closing, until the eggs just start to set on the bottom, 20 to 30 seconds. Close the top without locking it and cook until the eggs are set, 30 seconds to 1 minute longer.
Open the iron and, using a spatula, fold the okonomiyaki in half; transfer to a plate. Serve topped with the bacon, Kewpie, Sriracha, bonito and sliced scallions.
Look for Kewpie mayonnaise (which is made with rice vinegar, and very popular in Japan) and bonito flakes at Asian markets.