Heat the oven to 350 degrees F.
Heat an 8-10 inch cast iron skillet over medium heat. See note below.
Add the ground beef and taco seasoning and stir throughout cooking to combine, about 8-10 minutes.
Next, add in the onions and mushrooms, and continue stirring every 2-3 minutes for 5-6 more minutes.
Once everything is soft, add in the enchilada sauce and beans. Bring the mixture to a simmer and continue to stir every few minutes.
Add in 2/3 of each cheese and stir to combine.
Pour the mixture into a bowl and remove the skillet from the burner.
Add a large spoonful of the mixture to the bottom of the skillet, and spread it around so the tortillas don't burn.
Place one tortilla into the skillet and cover with a spoonful of the sauce mixture.
Add another tortilla and repeat the layering until you've used all of the ingredients, top with all of the remaining cheddar and cotija cheese.
Bake the casserole for 25-30 minutes and remove from the oven.
Sprinkle with cilantro and add a dollop of sour cream if desired.