In a small bowl, stir the paprika, cumin, garlic powder, cayenne pepper, salt, pepper, apple cider vinegar, honey, olive oil, tomato paste and Worcestershire sauce until well combined.
Place the onions at the bottom of a slow cooker, add the pork on top and pour the sauce over it, making sure to cover the entire piece of meat. Some of the sauce may drip to the bottom of the slow cooker.
Turn the slow cooker on and cook for 4 hours on high or 8 hours on low.
In the meantime, make the apple slaw by stirring together in a small bowl the Greek yogurt, apple cider vinegar, honey, dijon mustard, poppy seeds, lemon juice, garlic, salt and pepper together.
In a large bowl toss the apples, cabbage, carrots and green onions together. Add the slaw dressing and toss until completed coated. Place in fridge and let chill until ready to serve. This slaw will keep for a couple of days and is perfect for leftovers.
When pork is cooked all the way through, take it out of the slow cooker and let cool slightly. Shred pork into small pieces using 2 forks. Discard onions.
Add some or all of the sauce back into the shredded pork. I like a saucy pork sandwich, so I just added all of the shredded pork back into the slow cooker, but feel free to adjust sauce to your family's preferences.
To serve, cut buns in half, spoon a huge serving of pork onto the bottom bun, top with a spoonful of the apple slaw and top with the remaining piece of bun.