Combine first 5 ingredients in a large zip-top plastic bag. Add chicken to bag; seal bag. Marinate in refrigerator 8 hours.
Place roasted peppers and Italian dressing in a blender; process until smooth (dressing will be thick). Set aside.
Prepare grill. Remove chicken from bag; discard marinade. Sprinkle salt and pepper over chicken. Place chicken on grill rack coated with cooking spray; cover and grill 6 minutes on each side or until done. Cut each breast half diagonally into strips.
Divide salad greens evenly among six plates. Top each serving with 1 sliced breast half, 1/4 cup yellow pepper, 1/4 cup onion, 2 tomatoes, and 1/4 cup roasted pepper dressing.