Mix the flour, salt, sugar, and baking powder in a bowl. Then grate the peeled nagaimo and stir it in with the dashi. Let the batter rest for at least 1 hour, or overnight if easier.

Core the cabbage, slice it into 1/2-inch strips, and mince it. Wash and dry it thoroughly.

Chop the pickled red ginger and cut the pork belly into 4-inch pieces.

Add the eggs, tenkasu, and two-thirds of the chopped pickled ginger to the batter. Fold in the cabbage one-third at a time.

Heat oil in two large lidded pans over medium heat. Divide the batter into two circles about 6 inches across and 3/4 inch thick. Lay 3 slices of pork belly on top of each pancake. Cover and cook on medium-low for about 5 minutes.

Flip the pancakes carefully, then press gently to hold together. Cover and cook for about 5 minutes more, then flip once more and cook uncovered for 2 minutes.

Brush the pancakes with okonomiyaki sauce and zigzag with mayonnaise. Sprinkle with katsuobushi, aonori, green onions, and remaining ginger. Cut into wedges and serve hot.