Preheat oven to 350ºF.

In a saucepan, combine the soup, milk, and the 3/4 of the cheese, reserving the remaining 1/4 for topping the casserole. Once the cheese is melted, stir in the green chiles.

In a skillet, brown the beef with the onions. Add in the oregano, garlic powder and salt.

In a well greased 9×13 casserole dish, layer half of the tortilla strips. Spread 1/2 of the beef mixture on top, followed by 1/2 of the cheese mixture. Repeat layers. Sprinkle reserved cheese on top.

Bake in preheated oven until heated through and cheese is melted, about 30 minutes.  Let the casserole sit for 10-15 minutes before serving if you want the slices to hold together.