Preheat oven to 350°F. Grease 9x13 inch baking dish and set aside.
In a large skillet over medium heat, fry beef until fully cooked and no longer pink. Break up using a meat chopper or wooden spoon as beef browns. Drain (rinse if desired). Add beans, chilies, taco seasoning, and hot salsa and stir well.
Layer 4 noodles, ⅓ of the meat mixture, ⅓ of mushrooms, and 1 cup of cheese. Repeat layers, adding two more layers, ending with cheese. I had 5 noodles on my top layer of noodles.
In a medium bowl, mix water with mild salsa. Carefully pour over top of the cheese. Cover baking pan and bake 1 hour or until heated through.
Top with sour cream and sprinkle with remaining cheese. Bake, uncovered, 5 minutes. Let stand 10-15 minutes before cutting and serving.
Garnish with sliced olives, green onions, and chopped tomatoes if desired.
Notes
Refrigerate leftovers in a covered container for up to 3 days and freeze portions in freezer-safe containers for up to 1 month.
Reheat individual portions in the microwave.
Nutrition information does not include optional toppings.