Preheat the oven to 350°F (175°C).
In a large skillet, heat the vegetable oil over medium heat.
Add the diced onion and cook for 3-4 minutes until softened.
Add the minced garlic and cook for another 30 seconds until fragrant.
Add the ground beef to the skillet and cook, breaking it apart with a spoon, until browned and cooked through, about 7-8 minutes.
Drain excess grease from the skillet.
Stir in the cream of chicken soup, sour cream, milk, salt, black pepper, chili powder, and ground cumin into the beef mixture. Mix well and cook for 2-3 minutes until heated through.
Remove the skillet from heat and stir in 1/2 cup of shredded cheddar cheese and 1/2 cup of shredded Monterey Jack cheese.
In a 9×13 inch baking dish, spread half of the Doritos evenly on the bottom.
Pour the beef and cream of chicken mixture evenly over the Doritos layer.
Sprinkle the remaining Doritos over the beef mixture.
Top with the remaining shredded cheddar and Monterey Jack cheeses.
Bake uncovered in the preheated oven for 20-25 minutes or until the cheese is melted and bubbly.
Remove from oven and let the casserole rest for 5 minutes before serving.