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.

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.