For the most smoke production, soak wood chunks in enough water to cover for at least 1 hour before grilling. Drain wood chunks before using.
Thaw fish, if frozen. Rinse fish; pat dry. Make a pocket in each fish fillet by cutting horizontally from one side almost through to the other side. Fill with slices of smoked salmon and 2 teaspoons of the dill, folding salmon slices as necessary to fit. Brush fish evenly with lemon juice and top with the remaining 2 teaspoons of the dill. Sprinkle with salt and pepper.
Drain wood chunks. In a smoker arrange preheated coals, drained wood chunks, and water pan according to the manufacturers directions. Pour water into pan. Place fish, skin side down, on grill rack over water pan. Cover and smoke about 30 minutes or until fish flakes easily when tested with a fork. If desired, serve with Horseradish Cream.
In a small bowl stir together sour cream, green onion, horseradish, and dillweed.