1. Marinate the salmon in teriyaki sauce for at least half an hour or as long as overnight.
2. Preheat oven to 375 degrees Fahrenheit (190 degrees Celsius).
3. Place salmon on a parchment-lined baking sheet and bake for 12–13 minutes.
4. Meanwhile, prepare the mushrooms. Heat oil in a large frying pan, and add mushrooms. Sauté until softened. Add cream cheese and stir until just melted. Remove from pan.
5. Pour warm, creamy mushrooms over baked fish. Sprinkle with scallions and a generous amount of pepper. Serve warm.