Slice the napa cabbage and soak it in brine for 1 hour.
Rinse and drain the Napa cabbage thoroughly.
Prepare daikon, carrot, onion, and green onions.
Blend garlic, ginger, chilli flakes, and sugar into a fine paste.
Mix all the vegetables with the paste in a bowl and add fish sauce into it.
Pack the mixture into a jar and press it to remove air pockets.
Cover the jar loosely or use a fermentation weight.
Let it ferment at room temperature for 1 to 3 days.
Add some vinegar to the sauce, bottle it up, and store it in the refrigerator.
