Heat oven to 425 F. Place tenderloin on rack in shallow roasting pan. Roast about 30 minutes until internal temperature reaches 150 F. Let stand 10 minutes before slicing very thin. Also, place bacon on a sheet pan and cook until crispy. After finished cooking let extra bacon fat drain onto a paper towel before serving.
Mix together salad dressing and barbecue sauce; set aside.
Sauté onion slices in oil over medium heat until very tender and dark golden brown.
Place bottom half of each roll on baking sheet; spread with barbecue ranch dressing. Top with sliced ham, sliced pork tenderloin, caramelized onions, shredded cheese and crispy bacon. Place under broil until cheese is melted, 1 to 2 minutes.
Remove from oven, top with spinach and top of roll and serve warm.