1. Preheat your oven to 350°F (175°C) and grease a 9×13-inch baking dish.
2. In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté until translucent, about 5 minutes.
3. Add the shredded chicken to the skillet, sprinkle with taco seasoning, and stir to coat the chicken evenly.
4. In a large bowl, combine the cream of chicken soup, sour cream, and diced tomatoes with green chilies. Stir until well mixed.
5. Layer half of the crushed Doritos at the bottom of the prepared baking dish.
6. Spread the seasoned chicken mixture over the Doritos, followed by the soup mixture, ensuring even distribution.
7. Top with the remaining crushed Doritos and sprinkle the shredded cheese evenly over the top.
8. Bake in the preheated oven for 25-30 minutes, or until the cheese is bubbly and golden brown.
9. Let the casserole cool for a few minutes before serving, allowing the flavors to meld together beautifully.

Mama Lou always said the secret to a perfect casserole was patience—letting it rest for a few minutes after baking ensures every bite is a taste of harmony.