Preheat oven to 425°.
Cut a (36-inch-long) piece of parchment paper. Fold in half crosswise; open. Place fillets, slightly overlapping, in the center of right half of paper. Sprinkle with salt and pepper. Top with ginger, lemon, tomatoes, and onions.
Fold paper; seal edges with narrow folds. Slide packet onto a baking sheet; lightly coat packet with cooking spray. Bake at 425° for 15 minutes or until browned. Place on a platter; cut open.