Preheat the oven to 425°F. 4 pieces of parchment paper or aluminum foil about 12 x 18 inches

Fold each piece of parchment or foil in half, then open and lay flat. Oil or butter both sides of the inside surface of each piece. Set aside. Combine the carrot, celery, and onion. Using about half of the carrot mixture, place some over the bottom of each of the pieces of paper or foil. Salt and pepper the fish fillets and put one on each bed of vegetables. Top each fillet with some of the remaining carrot mixture. Fold the paper or foil over and seal by rolling the edges of each packet tightly. The finished packet will be about 6 x 9 inches. Place on a large baking sheet and bake for 10 - 15 minutes, depending on the thickness of the fillet. Serve, sealed, with a lemon wedge.