Brown ground beef in a pan.
Add onions, garlic, and oregano. Sautee until onions are soft.
Stir in taco spice.
Add tomato sauce and stock. Simmer for 10 minutes.
Lightly coat a baking dish with non-stick spray.
Ladle in enough sauce to coat the bottom.
Arrange 4 corn tortillas in the dish with slight overlaps.
Ladle in about half of the remaining sauce on top.
Sprinkle a cup of shredded cheese on top.
Layer in remaining corn tortillas.
Top with the rest of the sauce and cheese.
Cover the dish with aluminum foil and bake for 20 minutes at 350F.
Garnish with sour cream and chopped green onions to serve.