Combine the yogurt, buttermilk, mayonnaise, vinegar, curry powder, garlic, salt and some pepper in a medium bowl and whisk to incorporate. Combine the chicken, apple, grapes and watercress in a large salad bowl. Pour the dressing over and toss to thoroughly coat. Taste and adjust the salt, pepper and curry powder as desired. Arrange a lettuce leaf on each of 4 salad plates. Divide the salad evenly among the plates and top with chopped almonds.