Preheat the oven to 375°F (190°C).
Heat 2 tablespoons olive oil in a skillet over medium-high heat.
Add 1 red onion, chopped, and sauté 3–4 minutes until softened.
Add 1 pound ground beef (lean) and cook until no longer pink, breaking it up as you go.
Stir in 2 tablespoons Mexican seasoning (low sodium), remove the skillet from heat, and set the beef mixture aside.
In an 8×8 baking dish, spread 1/2 cup enchilada sauce (low sodium) evenly over the bottom.
Layer 4 corn tortillas (4") over the sauce, overlapping as needed to cover the bottom. Spread half of the beef mixture over the tortillas, then sprinkle 1 cup shredded cheese (Mexican blend) evenly over the beef.
Add a second layer: place the remaining 4 corn tortillas, spread the remaining beef mixture over them, sprinkle the remaining 1 cup shredded cheese, and spread the remaining 1/2 cup enchilada sauce over the top.
Bake in the preheated oven for 20–25 minutes, until the cheese is melted and bubbly.
Let the casserole cool for 10 minutes before cutting and serving.