Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with cooking spray or oil.
In a large skillet, heat the oil over medium heat. Add the oil, chopped onion, minced garlic, and sauté until softened, about 5 minutes.
Stir in the dried cumin, chili powder, salt, black pepper, and chopped green chiles. Cook for an additional 2 minutes, until fragrant.
Add the chicken, cheese, corn, beans, Rotel, and Greek yogurt (or sour cream) and mix until well combined. This will create a creamy sauce for the casserole.
In the prepared baking dish, spread a thin layer of the creamy sauce mixture on the bottom.
Arrange a layer of halved corn tortillas over the sauce, covering the bottom of the dish. Spread half of the chicken mixture evenly over the tortilla layer.
Repeat the layers: tortillas, remaining chicken mixture. Finish with one more layer of the halved tortillas over the top (Each layer will be 10 halves) Then top with the shredded cheese.
Cover the baking dish with aluminum foil and bake in the preheated oven for 25-30 minutes, or until the casserole is heated through and bubbly around the edges.
Remove the foil and bake for an additional 5-10 minutes, or until the cheese is melted and lightly golden brown. Mix the Greek yogurt crema in a bowl.
Once done, remove the casserole from the oven and let it cool slightly before serving.
Garnish with chopped cilantro, red onion, sliced green onions, Greek yogurt crema, and diced avocado.