Cut apples in half and remove the core with a melon baller. Chop apples into medium-sized pieces, leaving skin on.
In a bowl, toss apples with the cider vinegar. Fold in mayonnaise thoroughly. Season with salt and pepper to taste. Fold in walnuts, raisins, curry powder, celery, mint and red onion. Adjust seasoning. Refrigerate for at least 1 hour to allow flavors to incorporate. To serve, arrange 2 leaves of romaine lettuce per plate and spoon salad on top.