Slow-Cooked Shredded Beef Tacos

1-1/2 pounds beef chuck roast
1 medium onion, sliced
1 cup water
1 package taco seasoning mix
10 ounces taco sauce
1 can diced green chilies
1 package taco shells
Toppings: shredded cheese, lettuce, tomato, sour cream.

Place beef and onion in slow cooker. Combine water and
seasoning mix in a small bowl. Pour over beef and onion.
Cook on LOW for 6-8 hours or until tender. Remove meat to
cutting board: shred beef with two forks. Place beef in
large bowl. Stir in taco sauce and chilies. Fill warmed
taco shells with beef mixture. Top with lettuce, tomato,
cheese, and sour cream. Enjoy.