In a medium bowl or large ziplock bag, whisk together vinegar, honey, garlic, oil, Italian seasoning, salt, and pepper.
Add chicken and marinate, refrigerated, for at least 30 minutes.
In a small bowl, combine avocado, tomatoes, basil and an additional dash of salt & pepper.
Preheat grill to medium-low.
grill chicken about 6 minutes on each side, or until juices run clear and there is no pink in the center.
Serve topped with avocado/tomato/basil mixture.
Notes
As an option, make a second, smaller batch of the marinade and use it to baste the chicken while grilling. Do not use the marinade from the chicken for this as it has raw juice from the chicken in it.