Step 1: Preheat your oven to 375°F (190°C). Lightly grease a 12-inch cast iron skillet or a 9x13 inch baking dish.
Step 2: In a large bowl, combine the shredded cooked chicken, chopped onion, minced garlic, diced green chiles (undrained), cream of chicken soup, sour cream, milk, cumin, and chili powder. Mix well. Season with salt and pepper to taste.
Step 3: Warm the corn tortillas to make them pliable. You can do this by wrapping them in a damp paper towel and microwaving for 30-60 seconds, or by quickly dipping each tortilla in a shallow plate of warm enchilada sauce (not included in ingredients, but optional if you have some) or lightly frying them in a small amount of oil for a few seconds per side.
Step 4: Spread a thin layer of the chicken mixture onto each warm tortilla. Roll up the tortilla tightly and place it seam-side down in the prepared cast iron skillet. Repeat with the remaining tortillas and filling, arranging them snugly in the skillet.
Step 5: Pour any remaining chicken mixture over the rolled enchiladas. Evenly sprinkle the shredded cheese over the top of the enchiladas, ensuring good coverage.
Step 6: Bake for 30-35 minutes, or until the enchiladas are heated through, the sauce is bubbly, and the cheese is melted and lightly golden. For extra browning, you can broil for the last 1-2 minutes, watching carefully to prevent burning.
Step 7: Remove from oven and let rest for 5-10 minutes before serving. Garnish with fresh cilantro, diced avocado, or extra sour cream if desired.