I suggest making up some great big burritos.  Beef, beans, lowfat cheese, and guacamole....and load it up real good so you're eating minimal tortilla (use the really big tortillas; they're more efficient than multiple small tortillas).  
I like to use this slow cooker recipe for the beef:
Shredded Beef
3- to 3 1/4-pound boneless beef chuck shoulder or bottom round roast, cut into 4 large chunks 
1 medium onion, quartered 
3 whole cloves garlic, peeled 
1 teaspoon salt 
1/2 teaspoon pepper 
2 T. Adobo Chilies
2 T. green chilies
3/4 cup water 
In slow cooker, place onion, chilies and garlic; top with beef chunks. Sprinkle beef with salt and pepper; add water. Cover and cook on low 8 to 9 hours or until beef is tender. (No stirring is necessary.)   Remove the beef from the cooker, place onto a plate, and use two forks to pull apart the beef into shreds.