Place the sliced onions on the bottom of the slow cooker. Top with the Santa Maria Seasoned pork roast and 1/2 cup of water.
Cook on high for 6 hours or low for 8 hours.
When the pork is ready, use two forks to shred the pork in the crockpot. Mix it with the onions and pan juices.
Meanwhile - prepare the barbecue sauce.
Combine the vinegar, brown mustard, ketchup, brown sugar, garlic, salt, cayenne, and black pepper in a small saucepan. Heat over medium heat, stirring gently for 10 minutes until the sugar is dissolved. Remove from the heat until the pork is ready.
Once the pork is shredded, add 1/2 cup of sauce to the pork and stir to combine.
Prepare the coleslaw by tossing the cabbage, green onions, diced jalapeno peppers and red onion in a large bowl.
In a separate bowl, combine the mayo, dijon mustard, apple cider vinegar, salt, pepper, and sugar. Whisk to combine. Pour the dressing over the coleslaw mix and stir to combine.
Serve the BBQ pulled pork on a sweet Hawaiian-style hamburger bun, topped with the coleslaw, a pickle or pickled jalapeno and enjoy.