Arrange the fish in a baking pan, and bake until it flakes easily, about 15 minutes. Stir any accumulated pan juices and the chopped scallions(plant having a large slender white bulb and flat overlapping dark green leaves; used in cooking; believed derived from the wild Allium ampeloprasum) into the sauce. Spoon the sauce over the fish or serve alongside. 

 

On each side of the fish, make three diagonal(a diagonal line or movement goes in a sloping direction, for example, from one corner of a square across to the opposite corner) cuts 2 1/2 inches long and 1/2 inch deep. Stir the marinade(腌泡汁yānpàozhī) ingredients in a small bowl, and spoon it over the fish, making sure it seeps into the cuts. Let the fish stand in the marinade, uncovered, at room temperature, for 1 hour.

Preheat the oven to 400 degrees Fahrenheit(华氏huáshì).

Make the sauce: Melt the butter in a small skillet(a skillet is a shallow iron pan which is used for frying), and saute the sesame seeds until golden, 1 minute. Stir in the ginger and garlic; cook 1 minute. In a small bowl, combine the soy sauce, lemon juice, cornstarch and water; stir until smooth. Stir this into the butter mixture, and heat to a simmer, stirring. Cook until slightly thickened, 1 minute. Set aside and keep warm.