1. Place potatoes in steamer basket that has been set in large saucepan. Steam over boiling water until just tender, about 10 minutes. Remove steamer basket from water. 2. Prepare charcoal grill or preheat gas grill to medium-high heat. (Using a vegetable grilling rack will help keep potatoes from slipping through grates.) Brush potatoes with a little olive oil and grill until tender and tinged with brown, turning often, about 6 minutes. 3. Meanwhile, make dressing: In small bowl, whisk together vinegar, mustard, shallots and lemon peel. Slowly whisk in oil until blended. Stir in parsley.