In a medium mixing bowl, whisk together oil, vinegar and Hidden Valley Ranch Dip mix.
Add chicken pieces and turn to coat. Cover the bowl and refrigerate for 1 hour.
Preheat your grill.
Remove the chicken from the bowl, let the excess marinade drip back into the bowl. Discard the marinade.
Place the chicken on the grill.
Grill until cooked on both sides. (Time depends on the hotness of your grill. Check the chicken with a meat thermometer. It should read 165 degrees F.)
Remove the chicken from the grill and place on a cutting board. Let sit for 10 minutes.
Slice the chicken pieces lengthwise.
Slice open the sub rolls.
Place cheese on the bottom part of your roll. Top with sliced chicken. (I used 2 tenderloins per sub.) Top with tomatoes and peppers. Drizzle with Hidden Valley Ranch Dressing. Top with lettuce and the top part of your sub roll.