Combine first 3 ingredients in a small bowl, stirring well with a wire whisk.
Place fish in a 13- x 9-inch baking dish. Pour oil mixture over fish. Top fish evenly with tarragon and lemon slices. Cover and marinate in refrigerator 2 hours.
Place fish in a grill basket coated with cooking spray. Grill, covered, 5 to 7 minutes on each side or until fish flakes easily when tested with a fork.
Tip: Substitute any fresh herb for the tarragon in this recipe.