To make the Easy Teriyaki Sauce, whisk all the sauce ingredients in a small sauce pan and simmer on low for 3 minutes, until the sauce has thickened slightly.
Brush salmon fillets with 1 tablespoon of the cooking oil, season with salt and pepper. Heat a frying pan over high heat. and cook for 3-4 minutes on each side, until just cooked through. Remove the salmon to a plate to let rest..
Return the frying pan to the stove on medium-high heat. When hot, add the remaining 1/2 tablespoon of cooking oil. Add the mushrooms and saute for about 2 minutes. Reduce heat to low and add the teriyaki sauce, let simmer for 1 minute. Serve the teriyaki mushrooms on top of the salmon. Garnish with green onion, if desired