I'm not sure there's anything easier than this crock-pot shredded beef.
This recipe is a variation from one taught to me by a friend's mom while we were on a ski trip in Big Bear in the 80's. Thank you, Mrs. Loftus!
She cooked the roast on the stove top and added more seasonings. I've found the jarred salsa has all the seasonings I need. If I want things spiced up a bit, I handle that with add-ins such as onions, cilantro, cheese, sour cream, salsa, olives, tomatoes, etc.
To stretch this shredded beef even further, you can always add refried beans to the burritos!