Tijuana Torte Casserole

1 pound ground beef
2 cups thinly sliced onions, divided
2 cups sliced fresh mushrooms
2 cloves garlic, minced
1 (4 ounce) can diced green chiles
2 teaspoons oregano
Salt, to taste
1 (14 1/2 ounce) can tomatoes
1 teaspoon red pepper flakes
6 corn tortillas
3 cups shredded Cheddar or Monterey jack cheese
Chopped parsley

Preheat oven to 350 degrees F.

In large skillet, saut