In a small combine water, sesame oil, brown sugar, garlic, ginger, soy sauce and vinegar. Stir until the sugar is dissolved.
In a large zip top bag place the fish and pour the marinade over. Let sit in the fridge for up to 45 minutes.
When ready to cook heat a couple tablespoons oil in large skillet over medium high heat. Place the fillets top side down. Cook for 4-6 minutes a side, depending on the degree of doneness you prefer. I prefer medium well so that normally takes about 5 minutes a side depending on the thickness of the fillet.
While the fish is cooking pour the used marinade in a small sauce pot. Whisk in the teaspoon of corn starch. Bring to a boil and let reduce until the sauce becomes thick. If it gets too thick just thin out with a tablespoon or two of water.
Serve the fillets over steamed rice and drizzle the reduced sauce over top.
Notes:
* If you are using this sauce for chicken you can marinate longer-1 hour to over night.