Make teriyaki sauce: In a small saucepan simmer sauce ingredients, stirring until sugar is dissolved, until reduced to about 1/2 cup and cool to room temperature in a metal bowl set in a larger bowl of ice and cold water.
In a baking dish large enough to just hold salmon steaks in one layer marinate salmon in sauce, turning to coat, 15 minutes.
While salmon is marinating, in a large saucepan of boiling salted water blanch vegetables 2 minutes, or until crisp-tender, and drain in a colander.
Transfer vegetables to a bowl of ice and cold water to stop cooking and drain well.
In a 10-inch heavy skillet (preferably cast iron) heat oil over moderately high heat until hot but not smoking.
Transfer salmon to skillet with a metal spatula, letting excess sauce drip off and reserving, and reduce heat to moderate. Saute salmon, turning once, until just cooked through and browned well, about 2 1/2 minutes on each side, and transfer to 2 plates.
Pour off oil and cook vegetables, stirring, 1 minute. Add reserved sauce and boil, stirring, 1 minute, or until thickened.
Spoon vegetables and sauce over salmon and garnish with scallion greens.