In a skillet add the ground beef and onion. Season with the cumin, oregano, chili powder, garlic powder, salt, and pepper.
Cook the ground beef until it is no longer pink and the onion is tender. Drain any grease.
While the ground beef is browning, in another skillet add the butter and melt. Add the flour and stir until the butter and the flour is combined and smooth. Pour in the broth and milk cook until the mixture becomes thick. Stir in the salsa and sour cream.
Add the ground beef to the salsa mixture and mix well. Preheat oven to 350 degrees F.
Cut 8 corn tortilla shells into 1-inch strips. Place half of the strips in the bottom of a 9 x9-inch baking dish.
Top the corn tortilla shells with the ground beef mixture. Sprinkle one half of the cheese on top of the ground beef. Repeat these steps one more time.
Bake in the preheated oven until the cheese is melted and lightly browned. When serving top with additional sour cream and tomatoes if desired.