In a baking dish combine all ingredients for the beef, wrap tight with foil and bake for 45 minutes or until beef is tender.
Using 2 forks pull in opposite directions to shred the meat and mix into then mix into the sauce.
Place beef mixture into taco shells, top with avocado and salsa verde.
Salsa Verde
Place tomatillos in a pan and cover with water. Bring to a boil and turn down to a simmer for 5 minutes. Remove tomatillos with a slotted spoon and place in blender or food processor along with onion, garlic, cilantro, lime juice, and a pinch of salt and pepper. Blend until smooth. Serve warm.