Mix the ingredients for the sauce and set it aside.
Okonomiyaki
Whisk the eggs together with the water, crumbled stock cube, breadcrumbs, salt and pepper.
Combine the vegetables and fold the egg mixture into them.
Heat 2 frying pans with a little oil and divide the vegetable mixture between them. Press the mixture out into rounds with a palette knife – it should be a good 1 cm thick, perhaps a little more.
Fry for about 4 minutes over a medium heat, then turn and fry for a further 4 minutes on the other side.It is important that the pancake has "set" before you turn it, so it doesn't break apart. I like to turn them by sliding them out onto a plate, holding the pan upside down over the plate and flipping them back into the pan. But they can also be turned with a wide palette knife, fish slice or similar.
When your okonomiyaki are done, top them with mayonnaise, okonomiyaki sauce and finely sliced spring onion, and sprinkle with chilli flakes and microgreens if you like.