Preheat oven to 350 degrees. Spray a non-stick skillet with non-stick cooking spray and heat on medium.
Add beef, onion and mushrooms and cook until meat is cooked through.
Drain if needed, I bought extra lean beef and there was no grease to drain today.
Add garlic and cook another minute.
Add beans, diced green chilies, corn, oregano, chili powder, garlic powder, cumin, pepper and kosher salt.
Spray a 9 x 13 pan with non-stick cooking spray.
Lay half of corn tortillas on bottom of pan.
Add half of the beef mixture and 1/2 c of cheese.
Layer remaining corn tortillas and top with beef mixture and 3/4 c cheese.
Bake in oven uncovered for 15 minutes.
After cooking sprinkle with diced avocado and lettuce. Slice and serve and add a dollop of sour cream on top of slice.