In a slow-cooker, add pork. In a medium bowl, combine barbecue sauce, brown sugar, juice of 2 limes, garlic powder, chili powder, and cayenne, then mix together into a thick paste and spread all over pork.
Cook on high for 5 to 6 hours or on low 8 to 9 hours, until tender, then shred.
When ready to eat, make pineapple slaw: Combine cabbage, pineapple, remaining lime juice, olive oil, red onions, green onions, and red pepper flakes.
Top tortillas with shredded pork and pineapple slaw.
If you don't have a slow cooker, place the pork in a roasting pan and cook at 110 - 120C for 5 - 6 hours or until falling apart when pulled with forks. If the pork starts to brown too much while cooking cover loosely with foil.