In small saucepan, boil first 5 ingredients until sauce is reduced to 1/3 cup, 5 minutes. Season fish. In skillet, cook fish in oil over medium until opaque in center, 3 minutes per side. Spoon sauce over fish. Top with cilantro.
MAKE A SPLASH: Fish sauce isn't just for Asian dishes like this one. A dash of the stuff adds salty flavor to sautéed greens, marinades, tomato sauce, and more. (We promise it won't make your sauce taste fishy!)