Over medium heat in a saucepan combine 1 cup water, soy sauce, brown sugar, sesame oil, ground ginger, onion powder and minced garlic. Cook until heated through about 1-2 minutes.
In a small bowl mix the cornstarch with the 1/4 cup water until dissolved.
Add the cornstarch mix to the saucepan whisking so it doesn't lump. Cook until the sauce has thickened about 5-7 minutes.
If the sauce is too thick add a tablespoon or two of water to thin it out.
Notes
After adding sauce to your main dish, sprinkle with sesame seeds for garnish.