Crumble the feta into a food processor, add the Greek yogurt and olive oil, and process for several minutes, until smooth and creamy. Store in the refrigerator until ready to assemble the salad.
Preheat your grill to medium high heat. Place each peach half on the grill, cut side down, for 4-5 minutes. Flip over and grill for another 4-5 minutes, or until caramelized and juicy. Alternatively, you can roast them cut side up on a baking sheet for 20-25 minutes at 425°F, or until tender.
Place arugula on four small salad plates or two large ones. Top with one or two peach halves (one for a side or appetizer salad, two for a main course salad), then dollop about two tablespoons of the whipped feta on top of each peach half.
Make the dressing. Combine the ingredients in a blender or food processor and puree until smooth. Season to taste with salt and pepper. Store in the refrigerator.
Sprinkle each salad with the nuts and drizzle with Blueberry Balsamic Vinaigrette.