one 9-by-13-inch aluminum foil baking dish; one 9-by-13-inch glass baking dish
For the sauce: In a saucepan over medium heat, combine the vegetable oil and flour. Cook, whisking, until it begins to bubble; let it bubble for 1 minute. Pour in the enchilada sauce, chicken broth, cumin and some salt and pepper. Raise the heat and bring to a boil. Reduce to a simmer while you prepare the meat.
For the meat: Brown the ground beef with the garlic and onions in a large skillet over medium-high heat, 5 to 8 minutes. Drain the fat and stir in the cumin and salt to combine. Stir the meat into the simmering sauce and shut off the heat.
For the casserole: Preheat the oven to 350 degrees F. Lightly grease one 9-by-13-inch aluminum foil baking dish and one 9-by-13-inch glass baking dish with cooking spray.
Break up the chips by crushing the bag slightly with your hands. Make sure not to over crush the chips; you're looking for pieces, not crumbs. Mix together the cheeses in a medium bowl.
Divide a third of the broken chips between the prepared baking dishes. Top each with a quarter of the beef mixture and 2/3 cup of the cheese. Repeat, adding another layer of chips, beef mix and cheese to each. Finish by dividing the remaining chips between the baking dishes. Top each with 2/3 cup cheese.
Cover the glass baking dish with foil and bake for 25 minutes. Remove the foil and continue to bake until bubbly, another 15 to 20 minutes.
For the toppings: Top the cooked casserole with the shredded romaine, diced Roma tomatoes, sour cream and sliced black olives and green onions before serving.
Allow the aluminum foil baking dish to cool completely while the other is baking. Once cool, wrap tightly in plastic wrap and foil. Transfer to the freezer.
To bake from frozen, preheat the oven to 350 degrees F.
Unwrap the baking dish and re-cover with foil. Bake, covered, for 35 to 40 minutes. Uncover and bake until bubbly, 15 to 20 minutes. Top with another batch of the toppings.
The toppings listed are enough for one casserole. When you bake the second casserole at a later date, prepare the same amount of toppings.