Place first 5 ingredients (pork loin through red bell pepper) in a slow cooker.
In a food processor, blend together remaining ingredients (tomatoes through crushed red pepper flakes); pour mixture over pork and veggies in the slow cooker, making sure they’re entirely saturated.
Cover and cook on LOW for 8 to 10 hours. Shred pork with two forks and blend with slow cooker juices.
Fill large Romaine lettuce leaves with shredded pork, veggies and some slow cooker juices.