Use a sharp knife to halve the fresh pineapples lengthwise, crown and all. Remove hard core from pineapple. Cut out pineapple meat, leaving shells intact. Set shells aside.
Remove eyes from the pineapple meat. Cut pineapple into chunks, reserving 3 cups (refrigerate remaining pineapple for another use).
For salad, combine torn romaine, cubed ham, orange sections, Swiss cheese, and reserved pineapple chunks; toss lightly. Spoon into pineapple shells.
For dressing, stir together yogurt and orange juice. Serve dressing with salads.