Place the pork roast in a large slow cooker. Add the sliced onions, minced garlic, chopped chipotle peppers, salt, ground cumin, and just 1 can Old El Paso Red Enchilada Sauce. Cover the slow cooker and turn on high for 3-6 hours, until the pork roast in fork-tender. Shred the meat in the sauce with two forks. (This step can be done several days ahead.)
Preheat the oven to 350 degrees F. Cut the rolls in half horizontally. Place the bottom halves in a 9x13-inch baking dish. Top each roll with a heaping portion of shredded pork. Then place 2 squares of muenster cheese on top of the pork, followed by 2-3 pickled jalapeños. Place the roll tops on the sandwiches.
Bake the sandwiches for 5-8 minutes. Then pour the remaining can of Old El Paso Red Enchilada Sauce over the tops of the sandwiches and bake for another 5 minutes. Serve warm!