Prepare the Red Onion (1) and Red Cabbage (1) into thin slices with a mandoline or knife. Slice the Red Chili Pepper (2) thinly.
Fill a bowl with the prepared vegetables and cover with Rice Vinegar (3/4 cup), Apple Cider Vinegar (3/4 cup), Salt (1 tablespoon), Ground Black Pepper (1 tablespoon), and Olive Oil (2 tablespoon). Leave to pickle whilst you prepare the rest of the meal (at least 20 minutes).
To make the tartar sauce, roughly chop the Pickles (2) and Capers (2 tablespoon). Combine with the Japanese Kewpie Mayonnaise (7 ounce) along with the Lemon (1), Granulated Sugar (1/2 cup), Salt (1 teaspoon), and Ground Black Pepper (1 teaspoon). Chill until ready to serve.
Heat the Neutral Oil (4 cup) in a heavy saucepan until it reads 350 degrees F (180 degrees C) on a thermometer.
Combine the Potato Starch (1 ounce), Salt (1 teaspoon), and Ground Black Pepper (1 teaspoon) with a fork, in a wide tray. Coat the White Fish Fillet (4) on both sides with this mixture.
Fry the fish for 5-8 minutes until the internal temperature is 145 degrees F (62 degrees C). When the fish is done frying, drain over a wire rack and season with salt immediately.
To toast the burger buns, Butter (2 tablespoon) both sides and place the Buns (4 piece) down on a hot grill for 2 minutes each side or until golden brown.
Assemble the fish burger and serve with a side of slaw, extra tartar sauce and fries of your choice.