In a small bowl, mix together the paprika, garlic powder, cumin, chili powder, salt and brown sugar. Rub this all over the pork.
Heat a large skillet or pot with about 1 to 2 tablespoons oil over medium-high heat. Brown the pork shoulder on all sides about 3-4 minutes per side.
Place pork shoulder in the slow cooker with the onions and cook on the low setting for 8 hours.
Serve on toasted buns with coleslaw.
