Heat 3 tablespoons of the oil in a large skillet.
Brown meat with half the garlic powder and cumin, then remove with a slotted spoon and put in a 6- or 8-quart stockpot.
Add onions and chiles to the skillet with the remaining oil and sauté until soft.
Transfer to the stockpot.
Add all the remaining ingredients to the stockpot and bring to a boil.
Cover, reduce heat, and simmer 1½ to 2 hours, stirring occasionally. Serve with flour tortillas.