Put cabbage, green onion, pork, dashi powder, tenkasu, flour, water, eggs, salt, and pepper in a large bowl. Feel free to substitute a different type of meat or add other vegetables. If you don't have an ingredient, you can omit it, but at the minimum you need eggs, flour, water, and some sort of vegetable to mix in.
Mix everything until combined. The mixture should resemble a thick pancake batter.
Heat oil in a skillet, pan, or griddle. Scoop about 1/3 cup of batter into the hot pan and smooth out into a 4 inch circle. I can fit four okonomiyaki pancakes comfortably in my 12 inch skillet.
Cook on medium heat for about 4-5 minutes and then flip, cooking for another 3-4 minutes on the other side or until cooked through and lightly browned.
Remove okonomiyaki from pan. Spread okonomiyaki sauce on top.
Squeeze Japanese mayonnaise in a stripe pattern across the tops of the okonomiyaki. For the decorative pattern, use a toothpick or butter knife to draw vertical lines down the tops (see pictures/video).
Top with aonori and bonito flakes, if you have it. Okonomiyaki are best served freshly made, but you can keep leftovers in the fridge without the sauces on top for 1-2 days.