Spread the nuts on a baking sheet and toast in the oven for 8 to 10 minutes. Cool and break the nuts up into small pieces.
Whisk the yogurt, mayonnaise, parsley, honey, and lemon zest in a large bowl and season generously with pepper.
Halve, core, and cut the apples into 3/4-inch pieces, leaving the skin intact. Add the apples, celery and raisins to the bowl, and sprinkle with the lemon juice; then toss with the dressing. Cover and refrigerate if not serving immediately.
When ready to serve, toss walnuts into the salad. Arrange the lettuce leaves on a large platter, or divide them among 4 salad plates. Place the salad on the lettuce and serve.
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