Peel the radish, rinse in cold water, and pat dry. Cut it into 1 inch cubes and put it into a very large bowl. Add salt and sugar and mix well. Set aside for 30 minutes. The radish will release a lot of liquid during this time. Drain the juice from the radish into a measuring cup. Add the minced garlic, ginger, green onions, fish sauce, hot pepper flakes, and β cup of the juice from the radish.
Mix well until the seasonings coat the radish cubes evenly. Put the radish into a glass jar or dish for storage.
This can be eaten right away or stored in the refrigerator. You can also let it ferment by keeping it on the counter for a few days. When it starts to ferment, you will see little bubbles and the radish will start to smell stronger and sour. Once this occurs, store it in the refrigerator.
Notes
You can cut down the hot pepper flakes to β cup for a milder version. For a vegetarian version, you can replace the fish sauce with soy sauce.