Preheat oven to 400 degrees. Cut out four 12-by-17-inch pieces of parchment; fold each in half crosswise to form a crease, then open.
Combine soy sauce, ginger, and lemon juice, and toss with mushrooms. Divide evenly among 4 parchment pieces, arranging mixture on 1 side of each crease. Lay 1 salmon fillet on top of each pile. Season each with 1/8 teaspoon salt and the sesame oil. Fold parchment over ingredients; make overlapping pleats to seal.
Bake on 2 baking sheets (2 packets per sheet) for 10 to 11 minutes for medium-rare or 12 minutes for medium. Unwrap; sprinkle with sesame seeds. Top with pea shoots.