Soak the cedar plank in cold water at least 2 hours. Preheat your barbecue to medium-high. Place the shrimp, 2 Tbsp. of the butter, lemon juice, dill or tarragon, 1Tbsp. of the parsley, and garlic in a bowl. Season with salt and pepper and toss to combine. Set the sole flat on a work surface. Divide and set an equal amount of the shrimp mixture at one end of each piece of sole. Roll the sole around shrimp.
Remove the plank from the water and dry one side. Set the fish on the dry side of the plank. Brush the fish with the remaining butter. Set the plank on one side of the barbecue. Turn the heat underneath the plank to low and leave the other side of the barbecue set at medium-high. Close the lid and cook the sole for 12 to 15 minutes, or until just cooked through. Keep a spray bottle of water handy in case the board ignites. Set the plank on a serving tray, garnish with lemon slices, sprinkle with remaining parsley, and serve.