Place cashews on a baking sheet and toast for 10 minutes or until fragrant. Remove from oven; set aside to cool for 5 minutes, then finely chop. Set aside.
In a medium sized bowl, combine apples, balsamic vinegar, yogurt, sea salt, pepper, olive oil and toasted cashews; mix well to combine. Set aside.
In a large saucepan, bring 6 cups of water to a boil; add whole potatoes; cook for 10-15 minutes or until tender. Drain and cut into ½ inch cubes. Set aside to cool.
Combine arugula and cubed potatoes in a large serving bowl. Drizzle with yogurt dressing; gently toss to coat. Sprinkle with lemon zest. Place in the refrigerator until ready to serve.