Rinse the fish fillets and set aside. Preheat the oven to 425 degrees F.
For each fillet, fold a 12 x 15-inch piece of parchment paper in half. Open the parchment on a flat working surface and place fillet on one side of the center fold.
Top the fillet with 1 1/2 teaspoons of the chopped basil, 1/2 teaspoon of the chopped thyme or other herb of your choice, a sprinkling of salt and pepper, and 1 to 2 teaspoons of lemon juice.
Cover with a slice of tomato, 1 or 2 slices of lemon or lime, and a sprig of the fresh herb of your choice, and sprinkle on a teaspoon of capers, if desired. Fold the parchment over the fish and then, starting at one end and working your way around to the other end, carefully fold the cut edges twice (or three times if you prefer a crimped edge) to form a sealed packet.
Place the packets on an unoiled baking sheet and bake for 15 to 20 minutes-slightly longer for very thick fillets. The packets will become puffed and golden brown. Avoid the steam as you open a packet to check that the fish is cooked. When the fish flakes easily with a fork, open the packets and serve.