Because parchment paper traps in steam during cooking, the fish stays moist without the addition of oil or butter.
Preheat oven to 450 degrees. In a medium bowl, whisk together 2 tablespoons fresh lemon juice, 1 teaspoon coarse salt, and 1/4 teaspoon ground pepper. Add 3 large julienned carrots and 1/2 head shredded Napa cabbage; toss to combine.
Set four 15-inch squares of parchment on work surface. Use a slotted spoon to mound carrot mixture on one side of each sheet; reserve liquid in bowl. Roll 4 salmon fillets (1 1/2 pounds total) in reserved liquid. Place a fillet on each pile of vegetables; season with salt and pepper.
Fold parchment over contents; pleat edge to seal, forming a half-moon. Bake on a baking sheet 20 minutes. To serve, cut paper with kitchen scissors to open.