Place cubed chicken, sliced onion and sliced green pepper in a gallon-sized resealable bag.
In a mixing bowl, whisk together vinegar, lime juice and salad dressing mix.
Pour over chicken and vegetables and seal bag.
Refrigerate for at least 3 hours.
After chicken and vegetables have marinated, heat olive oil in a skillet over medium heat and saute until vegetables are soft and chicken is cooked through. Serve chicken and vegetables in tortillas and top with sour cream, cilantro and salsa.