Place pork roast in the slow cooker; add water, sliced onion, salt and pepper and garlic cloves. Cover and cook on low for about 9 to 11 hours, or until very tender. Drain all juices off, discard any fat and bone. Shred or chop pork. Continue cooking on high for about 1 hour.
Prepare onion topping by adding 1-2 tablespoons of oil in nonstick skillet over medium high heat. Add onions to pan, salt and pepper to taste. Continue to cook for approximately 10-15 minutes, or until soft. Add 2 teaspoons of chipotle chili powder and a couple of dashes of Tabasco Chipotle sauce to onions.
Combine and continue to cook for another 10 minutes. If onions are sticking to bottom of pan, deglaze by adding a couple of tablespoons of apple cider vinegar to pan.
Serve shredded pork on potato rolls with your favorite barbeque sauce; top with caramelized chipotle onions.