Add the olive oil and onion to a large, hot skillet. Sauté the onion until softened, then add the ground beef. Cook, stirring and breaking up the meat, until browned. Drain any excess fat.
Add the garlic powder, onion powder, oregano, and taco seasoning and mix thoroughly.
Stir in the diced green chiles.
To the crock layer half of the meat mixture, one of the cans of enchilada sauce, half of the corn, half of the black beans, half of the tortilla pieces, and half of each of the cheeses.
Make a second layer of each of the ingredients in the same order: meat, sauce, corn, beans, tortillas, and cheese.
Cover, and cook on low 4-6 hours or on high for 2 1/2-3 hours.
Serve with Optional Garnishes: Top each serving with sour cream, salsa, black olives and green onions, avocado or any combination, as desired.