For the dressing: In a small mixing bowl stir together yogurt, pomegranate juice, vinegar, lemon zest, stevia or honey, and salt until well combined. Cover and chill until ready to serve.
For the salad: Sprinkle grapefruit with stevia and set aside. Divide kale among four salad bowls.
Top each serving with strawberries, watermelon, grapefruit, pomegranate arils, walnuts and feta cheese. Drizzle each salad with dressing.