Grate the fresh ginger to get about 2 tablespoons.
Combine the grated ginger, soy sauce, sesame oil, minced garlic, and sugar in a bowl. Stir well to combine.
Add water to the mixture. Stir to reach the desired consistency. Optionally, add chili flakes for a bit of heat.
Let the sauce chill in the refrigerator for at least 30 minutes. Allow the flavors to meld together.
Taste and adjust the seasonings if needed. Drizzle over cold chicken, or serve as a dipping sauce.
Garnish with sliced green onions for extra flavor.