Move the oven rack to the middle position and preheat the oven to 350 degrees F. Spray a 9x13x3-inch pan with nonstick cooking spray, and set aside.
In a skillet over medium-high heat add the olive oil. Once shimmering add the onion and sauté, while stirring constantly, until translucent and the sides of the onion begin to brown, about 5-6 minutes. Add the garlic and cook until fragrant, about 1 minute.
Pour the onion mixture into a large mixing bowl along with the shredded chicken, cream soups, green chile sauce, cumin, salt and pepper; stir to combine.
Lay 4 corn tortillas into the bottom of the prepared pan. Spread 1/3 of the chicken mixture over the tortillas, followed by 1 cup of the cheese, and 1/3 of the tomatoes and green onion. Continue this layering of tortillas, chicken mixture, cheese, tomatoes and green onion 2 more times, but on the last layer DO NOT ADD THE CHEESE! Instead, just layer the tomatoes and green onions on top of the chicken mixture.
Mix together the remaining 1 cup of shredded cheese and chopped fresh oregano, and set it aside for later.
Cover the green chile enchilada casserole with foil and cook for 30 minutes. Take the foil off and then layer the remaining 1 cup of cheese over the top. Cook uncovered for 15 minutes. Let the enchiladas stand for 10 minutes before serving.
Serve with chopped tomatoes, chopped green onions, chopped oregano, shredded lettuce, and/or sour cream (all optional).
Note from the recipe’s creator:
This is the recipe that I use but I change it around sometimes. Sometimes I add grated zucchini. Sometimes I won’t add the cream of mushroom soup and just add some sour cream instead and use sharp cheddar cheese. I mostly use green chile from my freezer that I have peeled myself. The last time I made it I added a layer of fresh mushrooms on top.