1bottletomato sauce-or can of tomatoes, blitzed w/immersion blender
The day before you are going to cook your pork roast, mix up the rub and massage it into the meat - combine salt, black pepper (half of it), chili flakes, mustard powder, garlic powder, onion powder, chili powder and brown sugar. If you have a little food processor to combine, that would be awesome; if not, just stir to combine. Place the fat-trimmed pork on a dish and rub the mixture all around meat. Cover and place in the refrigerator until the next day when you are ready to put in the slow cooker.
Thinly slice onions and place on bottom of slow cooker; add remaining black pepper. Top with cider, tomato sauce and garlic. Carefully place the pork roast into the slower cooker, cover and cook on high for about 5 hours.
Once cooked, remove the roast from the slow cooker. The meat will literally be falling of the of the bone it'll be so tender! Place in a large bowl for shredding. Cover with foil.
Strain onions from sauce and place to one side.
Remove sauce from slow cooker and place in a pot and on the stove top simmer on medium low for about 30 minutes or so until it reduces slightly and thickens to about half.
Using two forks, shred pork; I like to leave some chunkier pieces in there for texture. At this point, you can mix the reduced tomato sauce mixture throughout the pork or you can leave for topping on the sandwich; it's pure preference.
Now, it's time to assemble your sandwich! On nice warm buns place a good serving of pork, top with reserved onions, sauce (if didn't mix through previously), cabbage, red onion, cilantro and feta. Enjoy!