Whisk together the yogurt, mayonnaise, lemon juice, scallions, curry powder, 1/2 teaspoon salt and a few grinds of black pepper in a medium bowl. Add the chicken, pecans, parsley, celery and raisins and fold to combine. Cover and refrigerate until ready to use (up to 3 days).
Core the apples and cut each into six to eight 1/4-inch thick rounds, for a total of 16 rounds. Arrange a lettuce leaf on 8 apple rounds and top each with about 1/4 cup of chicken salad. Sandwich with the remaining apple slices. Serve immediately.
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