Prep the veg - Peel the daikon and cut it into 2-inch matchsticks. Set aside. Peel the garlic, then using a rasp, grate the garlic into a medium bowl. Destem and finely chop the scallions. Set aside
Make the marinade - Add the gochugaru, fish sauce, sesame oil, and salt to the bowl with the grated garlic. Whisk to combine. Stir in the daikon, to coat.
Marinate - Top the salad with the chopped scallions, cover the bowl, and stash it in the fridge for at least 30 minutes.
Serve - When ready to serve, pull the bowl out of the fridge. The daikon will have released a bit of moisture, so stir the mixture again to evenly distribute the marinade and the scallions.