Combine the plain Dannon Oikos Greek nonfat yogurt, vinegar, honey, and gingerroot in a medium bowl.
Add the chicken, walnuts, and apple. Mix well. Gently stir in the grapes until just combined.
OPTIONAL: Seed and scoop out some of the flesh from the cucumber halves using a rounded teaspoon or melon baller. Divide the chicken salad among the cucumber boats.
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