Place the sliced onions and minced garlic at the bottom of the slow cooker. Pour chicken brother over the top.
In a small bowl, combine brown sugar, chili powder, salt, pepper, and cumin. Rub over the pork roast. Place roast in slow cooker and set on low for 8-10 hours.
Remove roast from slow cooker and shred using forks. Combine with BBQ sauce and keep warm until ready to serve.
For the Salsa:
Combine ingredients in a bowl. Squeeze lime over the salsa. Add salt and pepper to taste.
Cut buns in half and toast for 5 minutes. Fill with pulled pork and salsa.