Immerse and soak plank in water 1 hour; drain.
Prepare grill, heating one side to medium and one side to high heat.
To prepare steak, sprinkle steaks with 1/2 teaspoon salt and 1/4 teaspoon black pepper. Place plank on grill rack over high heat; grill 5 minutes or until lightly charred. Carefully turn plank over; move to medium heat. Place steak on charred side of plank. Cover and grill 12 minutes or until desired degree of doneness.
To prepare sauce, combine parsley and remaining ingredients in a food processor, and process until smooth. Serve with steaks.