Trim fat, season with salt and pepper. Heat pan with olive oil and brown all sides of meat. Place browned meat in a slow cooker. Combine tomato sauce, water, onion, chipotle peppers, garlic, cumin and coriander. Pour over roast. Cook on high for 5 hours or low for 8-10.
Remove pork shoulder from slow cooker, set aside. Strain and reserve cooking liquid. Using forks shred pork. Stir reserved cooking liquid to shredded pork.