Heat oven to 425 degrees F. Place tenderloin on rack in shallow roasting pan. Roast about 30 minutes until internal temperature reaches 150 degrees F. Let stand 10 minutes before slicing very thin.
Meanwhile, mix together salad dressing and barbecue sauce; set aside. Saute onion slices in oil over medium heat until very tender and dark golden brown.
Place bottom half of each toasted roll on baking sheet; spread with barbecue ranch dressing. Top with ham, pork tenderloin, caramelized onions, shredded cheese and bacon. Place under broil until cheese is melted, 1 to 2 minutes.
Remove from oven, top with arugula and crowns of rolls to serve.