Preheat the oven to 170°c. Spread the walnuts in an oven proof tray and toast for about 10 minutes. You can dry roast lightly on tawa or pan. Let it cool, then finely chop.
Meanwhile, in a small bowl, cover the rose petals with cold water and let stand until softened, about 20 minutes. Drain the petals and squeeze dry. Alternately you can use fresh rose petals.
In a large bowl, whisk the yogurt with the ice water. Stir in the raisins, cucumber, mint, dill, chives, walnuts and rose petals and season with salt and pepper. Refrigerate until very cold, about 1 hour.
Serve the soup in shallow bowls, sprinkled with lemon zest with crushed black pepper.