In a large mixing bowl, combine flour, water (or dashi), and egg, whisking until smooth and lump-free. Fold in the shredded cabbage and chopped green onions, along with any additional ingredients such as protein or other vegetables.

Preheat your skillet or griddle over medium heat, coating it lightly with vegetable oil to prevent sticking.

Pour a ladleful of the batter into the heated pan, forming a circle approximately 1 inch thick. Allow it to cook undisturbed for about 4-5 minutes.

Carefully flip the pancake using a spatula, and cook the opposite side for another 4 minutes.

Insert a toothpick into the center of the Okonomiyaki; it should come out clean to confirm the pancake is cooked through.

Transfer the finished Okonomiyaki onto a cutting board and slice it into wedges. Top with a drizzle of Okonomiyaki sauce and mayonnaise, sprinkling bonito flakes if desired.