Cut the cabbage into quarters and remove the core. Separate the leaves and place in a large bowl.
Mix the salt and water together and pour over the cabbage, making sure all of the cabbage is submerged. Marinate the cabbage for 1 to 2 hours. Drain and rinse the cabbage thoroughly. Place in a colander and press down to get as much liquid out of it as possible.
Meanwhile, combine the garlic, ginger, fish sauce, chili powder, sugar, and sesame oil in a small blender or food processor. Puree until smooth. Place your cabbage into a large bowl and toss with the sliced scallions and radish. Pour the dressing over the salad and mix well to ensure all of the leaves are coated.
Marinate for at least one hour before serving. This salad will keep and improve for up to a week in the fridge.