In a large skillet, heat oil at medium heat. Add mushrooms, leeks and pepper and cook about 8 minutes or until veggies have soften. Put the salmon pieces on the veggies in the skillet.
Meanwhile, in a small bowl, mix ginger, soy sauce, sesame oil and garlic. Spread the mixture on the salmon. Cover and cook for about 10 minutes or until the flesh is easy to flake with a fork. Sprinkle with green onion. Serve with quarters of lemon.