Combine salt, chili powder, oregano, garlic powder and onion powder.
Sprinkle seasoning on all sides of beef and pat down to adhere to meat.
Place onion slices in bottom of slow cooker and add broth (or water).
Set seasoned roast on top and cook for 8-9 hours on low or 4-5 hours on high, or until fork-tender.
Remove excess liquid, leaving about 1 cup.
Shred beef with two forks or meat claws.
Notes
Flank steak, skirt steak or any less tender beef can be used. Can be cooked in a covered dutch oven on stove top at medium low heat for approximately 4-5 hours or until fork-tender.