Thaw the fish fillet, dry it well, rub on both sides with the lime juice and cut diagonally into approx. 4 x 3 cm pieces. Whisk the egg white and salt well and mix with the fish pieces. Cap the onions and garlic cloves at both ends, peel and cut into small pieces. Wash and peel the fresh ginger, cut across into pieces approx. 4 cm long. Cut the pieces lengthways into thin slices and cut them into strips. Work the strips crosswise into small cubes. Freeze unused cubes. Weigh frozen goods and allow to thaw.
Mix 1 tbsp of the tapioca flour with 1 tbsp of the rice wine. Mix the sugar with the rice vinegar, the remaining rice wine, the dissolved tapioca flour, the fish sauce and the orange juice to make the sauce.
Separate the pak choi leaves from the stalk, wash and blanch for 2 minutes. Wash the tomatoes and the grapes. Cut a tomato crosswise and place the grapes there. Line a serving bowl with the pak choi leaves and four of the tomatoes (see photo). Heat the frying oil to 200 degrees.
Roll the fish pieces in the remaining tapioca flour so that they are covered on all sides. Heat the sunflower oil in a wok, stir-fry the onion, garlic and ginger in it for a minute. Add the tomato ketchup and stir-fry briefly, deglaze with the sauce and fry for 30 seconds. Keep it warm and ready.
Fry the fish pieces in 2 portions for approx. 2 minutes until light brown, drain and place in the serving bowl. Drizzle over the sauce, finish garnishing with the rest of the tomato, serve warm and enjoy as a side dish.