Combine 1 1/2 cups cucumber, the buttermilk, yogurt, shallot, cilantro, garlic, crushed red pepper, and lemon-pepper seasoning in a food processor. Cover and process until mixture is smooth.
Transfer to a large bowl. Stir in cold cooked shrimp, radishes, vinegar, and the remaining 1 cup cucumber. Ladle into soup bowls. Sprinkle individual servings with walnuts.
Tip: To toast nuts, spread in a shallow baking pan lined with parchment paper. Bake in a 350 degrees F oven for 5 to 10 minutes or until golden, shaking pan once or twice.
3 lean protein, 1 1/2 fat, 1 vegetable