In a large bowl, combine the flour, salt, baking powder and sugar. Add the water and eggs and mix until smooth. Add the cabbage and spring onions and mix again.
Heat a small amount of oil in a medium size frypan. Add half the mixture and scatter the pork belly on top. Cook on low to medium heat for 15minutes. Carefully flip the okonomiyaki (I flipped it directly into another frypan), and continue to cook gently for another 15-20 minutes. Top with a thick layer of the sauce and bonito flakes.
Repeat this process with the remaining mixture.