Quarter the dragon fruit lengthwise. Work your finger under the skin, pull it back and peel it away in 1 piece. Cut each quarter into 1/4-inch-thick triangles.
Whisk together the yogurt, mayonnaise, lemon juice, honey, ginger and salt in a large bowl. Add the apples, grapes, 3/4 of the dragon fruit pieces and 3/4 of both the cilantro and the cashews. Toss to combine, and refrigerate until chilled, about 1 hour.
Put a lettuce leaf in each of 4 small bowls, and top each with a scoop of salad. Garnish with the remaining dragon fruit, cilantro and cashews.
To determine the ripeness of dragon fruit, give it a gentle squeeze-it should have a slight give, like a ripe avocado.
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