Make the sauce – In a small bowl, whisk together soy sauce, sesame oil, mirin, brown sugar, garlic powder, onion powder, white pepper, and cornstarch until smooth.
3 tbsp soy sauce, 2 tbsp toasted sesame oil, 2 tsp mirin, 1 tsp brown sugar, ¼ tsp garlic powder, Dash of onion powder, Dash of white pepper, ½ tsp cornstarch