Whisk together mayonnaise, buttermilk, sour cream, garlic powder, salt and pepper in small bowl until smooth. Mix in parsley. Cover and refrigerate until ready to use.
Gently fold together pinto beans, white beans, kidney beans, ham, cheese and cucumber in large bowl. Fold in dressing until salad ingredients are evenly coated.
To serve, arrange lettuce over bottom and up sides of large bowl. Mound bean mixture in center.