Grilled Steak with Potato Salad

Name: Grilled Steak with Potato Salad
Ingredients: 1 1/2 pounds flank steak; 1/2 cup plus 2 to 3 tablespoons Vinaigrette; Olive oil, for grates; 1/4 cup reduced-fat mayonnaise; 2 teaspoons white-wine vinegar; 1/4 cup lightly packed flat-leaf parsley, finely chopped; 2 scallions, minced; 1 small garlic clove, minced; Coarse salt and ground pepper; 4 cups grilled or roasted new potatoes, cut into 1-inch chunks; 2 medium heads romaine lettuce (12 ounces each), cut crosswise into 1/2-inch pieces