1. Preheat oven to 375°. Sprinkle fillets with salt and pepper.
2. Cut parchment paper into 4 (13- x 9-inch) rectangles. Place 3 lemon slices crosswise in center of 1 parchment rectangle. Top with 1 fillet. Repeat with remaining lemon slices, fillets, and parchment paper rectangles. Sprinkle fillets evenly with carrot, dill, and parsley. Top each fillet with 1/2 Tbsp. butter. Fold 1 side of parchment paper over fillets; tuck excess parchment under fillets, pressing folds to form a crease.
3. Bake at 375° for 20 to 25 minutes or until fish flakes with a fork. Serve immediately.