Grilled Chicken and Pepper Salad

Prepare Balsamic Vinaigrette: In serving bowl, with wire whisk, blend all vinaigrette ingredients; set aside. Prepare Vegetables and Chicken: Cut each pepper lengthwise in half; discard stems and seeds. With hand, flatten each pepper half. In bowl, toss peppers and onion wedges with 3 teaspoons oil. Rub chicken breasts with remaining 1 teaspoon oil; sprinkle with salt and pepper. Place chicken on grill over medium heat. Cook chicken 12 to 15 minutes or until juices run clear when thickest part of breast is pierced with tip of knife, turning over once. While chicken is cooking, place onion wedges and peppers, skin side down, on same grill. Cook onion about 15 minutes or until golden, turning occasionally; cook peppers 18 to 20 minutes or until skins are charred and blistered. When onion wedges are done, remove from grill to plate. When chicken is done, transfer to cutting board. When peppers are done, wrap in foil and allow them to steam at room temperature 10 minutes or until cool enough to handle. While peppers are steaming, slice chicken breasts crosswise into 1/2-inch-wide strips. Remove peppers from foil; discard skins. Thinly slice peppers. Add peppers, chicken, onion, tomatoes, and arugula to bowl with dressing; toss gently to coat.