Preheat the grill to medium heat. Fold four sheets of foil in half crosswise to crease, and then unfold.
Combine the oil, soy sauce, ginger, garlic, lemon zest, orange zest and orange juice in a small bowl. Mix well to combine.
Place 1 fillet on one side of the crease on each sheet of foil and sprinkle with the salt and pepper. Divide the oil mixture equally among the fillets.
Working with 1 foil sheet at a time, fold the foil over the fillet and tightly crimp the edges of the foil to close the packets to create a papillote. Place each papillote on the grill and close the lid of the grill. Grill until the papillotes are fully puffed, about 12 minutes.
Carefully cut the foil to open and serve the fillets on the spinach and top with the Grilled Summer Relish.
Grilled Summer Relish:
Yield: about 2 1/4 cups.
Prepare the grill to medium heat. Brush the scallions, corn, bell pepper and squash on both sides with the oil. Sprinkle with 1 tablespoon salt and 1 teaspoon pepper. Grill the vegetables until slightly charred and just tender, turning often, about 5 minutes for the scallions, 8 minutes for the squash and pepper and 10 minutes for the corn. Transfer the vegetables to a cutting board and cut into 1/4-inch pieces. Cut the corn from the cob directly into a bowl and mix in the scallions, peppers and squash.
Meanwhile whisk the lemon juice, oil, vinegar, 1/2 teaspoon salt and 1/4 teaspoon pepper in a small bowl. Add the oil mixture to the bowl of vegetables; toss to coat.