If desired, marinate chicken in an additional 1/4 cup of balsamic vinaigrette for 1 hour. Grill approx. 5 minutes per side, or until cooked through. Allow to rest at least 5 minutes, then slice.
Layer spinach, chicken, cherries, blueberries and red onion. Top with goat cheese, pecan pieces and balsamic vinaigrette before serving.