Remove fat from meat. If necessary, cut meat to fit into a 3 1/2- or 4-quart slow cooker. Place meat in cooker. Add water, onions, jalapeno peppers, garlic, coriander, cumin, oregano, salt, and black pepper.
Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours.
Remove meat from cooker; discard cooking liquid. Using two forks, pull meat apart into shreds. To serve, spoon warm meat on lettuce. Top with cheese. Place salsa and sour cream on top (optional).