Mix together the corn, tomatoes, lemon peel, 1/8 teaspoon salt and 1/8 teaspoon pepper in a small bowl.
Lay out a 12- by 15-inch sheet of parchment paper or foil. Arrange one-quarter of the vegetables on 1 side. Fold a fish fillet into thirds and place on top of the vegetables. Top with one-quarter of the leeks, 1 sprig of thyme, 2 teaspoons of the wine, 1/2 teaspoon oil, and a pinch salt. Fold the other side of the parchment over the fish. Starting at 1 corner, fold the edges of paper over by 1/2 inch all around, overlapping the folds until sealed. Repeat with more parchment and the remaining fish, vegetables, wine and oil to make 4 packets. Place the packets onto a jelly-roll pan and bake for 15 minutes.
Meanwhile, place the spinach in a glass bowl and cover with a damp paper towel. Microwave on high until wilted, 2 minutes. Stir in 1/8 teaspoon salt and 1/8 teaspoon pepper.
Open the fish packets and serve with the spinach.
You can serve this dish with a side pasta salad. For each serving, cook 2 ounces of whole-wheat pasta, and then drain and toss with 1 cup cooked broccoli florets, 1/2 roasted red pepper, chopped, 1 tablespoon reduced-fat feta cheese and 2 tablespoons low-fat vinaigrette. Nutritional information per serving: 320 calories.