In a large oven-safe skillet, heat the oil. Brown the pork, garlic, and onion until brown.
Add chili powder, cumin, and salt. Cook 1 minute to toast spices. Stir in chilies and tomatoes.
Cover the skillet with a tight-fitting lid and bake for 2 – 3 hrs until fork-tender, adding water if necessary to ensure the meat stays moist.
Shred the pork and cook off any remaining liquid on the stove.
Serve in tortillas or taco shells with toppings of your choices.