Mix 1 tbsp of the brown sugar, paprika, minced onion, chili powder, salt, garlic powder, and allspice. Sprinkle 1 tbsp on this mixture into the bottom of the slow cooker, with the remaining being rubbed all over the pork roast. Add vinegar and remaining brown sugar tot he slower cooker and stir to mix. Then add the pork roast.
Cover and cook on low for 8 to 10 hours or until pork is fork tender. Remove pork to cutting board and shred. Return the shredded pork back to the crock pot and add in the scallions. Mix thoroughly.
Place 1/4 cup of BBQ on each dinner roll and serve.