Toast the Walnuts: Heat a small skillet over medium-low heat and add the walnuts. Toast them for about 7 minutes, stirring occasionally, until they become fragrant and golden brown. Once done, remove from heat and let them cool before chopping them finely.

Prepare the Cucumber: Slice ¼ of the cucumber thinly for garnish and set aside. For the remaining cucumber, cut it in half lengthwise and scoop out the seeds with a spoon. Chop the cucumber into small pieces.

Mix the Soup Ingredients: In a large mixing bowl, combine 2 cups of whole milk plain yogurt with ½ cup of ice water. Whisk until smooth. Stir in chopped cucumber, 1 cup of chopped fresh herbs, golden raisins, and toasted walnuts, followed by 1 teaspoon of kosher salt.

Chill the Soup: Cover the bowl and place it in the refrigerator. Allow the soup to chill for at least 1 hour, or up to 3 days if prepping ahead.

Serve and Garnish: Once chilled, divide the soup into individual bowls. Sprinkle with 1 teaspoon of sumac, and top with reserved cucumber slices and extra fresh herbs.