1. Whisk together first 5 ingredients. Gradually add oil in a slow, steady stream, whisking constantly until blended. Reserve 2 Tbsp. mixture; cover and chill. Stir bell peppers and next 2 ingredients into remaining vinegar mixture. Cover and chill 30 minutes.
2. Preheat grill to 350° to 400° (medium-high) heat. Remove vegetables from vinegar mixture; discard mixture. Grill vegetables at the same time, placing peppers skin side down on cooking grate. Grill vegetables, covered with grill lid, 6 minutes or until peppers look blistered and grill marks appear. Turn all vegetables, and grill about 2 more minutes or until crisp-tender.
3. Arrange vegetables in a single layer on a serving platter. Drizzle with reserved 2 Tbsp. vinegar mixture just before serving. Season with salt and pepper to taste.
*White wine vinegar may be substituted.
Prep the vinaigrette 3 days early, and wash and cut peppers 1 day ahead.