Preheat oven to 450℉. In a small bowl whisk soy sauce, mirin, sesame oil, sugar and ginger.

Place salmon in a roasting pan. Sprinkle fish with 1 teaspoon of the soy sauce mixture and rub it over the fish.

Roast the salmon, uncovered, for 12 minutes or until the fish can just be flaked with a fork and has changed color in the thickest part.

Remove from the oven and keep warm by lightly placing a piece of aluminum foil over it.

Rinse spinach leaves. With the water still clinging to them, place in a steamer and steam for 2 minutes, or until just tender. Drain.

Place clumps of spinach on a serving platter or on plates in a fairly thin layer. Arrange salmon next to or on top of the spinach.

Drizzle 1 teaspoon of soy sauce mixture on the salmon and pour the remaining mixture over the spinach.

Sprinkle with toasted sesame seeds.