Trim and discard any excess fat from the pork roast. In a small bowl, combine salt, cumin, paprika, black pepper, and red pepper; rub this mixture evenly over the pork.
Layer the sliced onion and bell pepper at the bottom of the slow cooker. Place the seasoned pork on top of the vegetables.
In a separate bowl, mix the barbecue sauce with the brown sugar until well combined, then pour the sauce mixture over the pork. Cover the slow cooker with a lid and cook on low for 8-10 hours.
Once cooked, transfer the pork to a cutting board. Remove and discard any remaining fat, then shred the meat using two forks.
Serve the pulled pork with the sauce spooned over it, or pile it onto buns for classic BBQ pulled pork sandwiches. Alternatively, enjoy it atop a bed of rice for a comforting meal.