Cut each tenderloin into 2-3 inch pieces. Set each piece upright so cut side faces up. Pound each piece into an approximate ½-inch steak. Arrange in a glass baking dish and cover with Italian dressing, coat each piece well, cover with plastic wrap and refrigerate for 2 to 3 hours.
Heat grill. Remove tenderloins from marinade to a plate. Slice onion and lightly drizzle with olive oil, sprinkle with salt and pepper. Have rolls split and ready to grill.
Grill pork until done, about 3 to 4 minutes per side. At the same time, grill red onions, flipping once until just lightly grilled. Place slice of provolone over two pieces of pork (or one piece of pork, depending on size) and close grill to melt. Remove to platter along with onions. Place split rolls on grill and toast lightly.
To assemble, place pork tenderloin piece(s) on bottom half roll, topped with some grilled onion, BBQ sauce and pickles. Top with other half of roll. Slice in half and serve. Enjoy.
Feel free to customize these to whatever toppings you like. I think it's very similar to a chicken sandwich but a nice change of pace.