Preheat oven to 350°F (175°C).

Brown ground beef and chopped onion in a skillet over medium heat.

Drain off any excess grease.

Stir in refried beans, tomato or taco sauce, green chilies, and taco seasoning.

Mix well until combined.

Lightly grease a baking dish.

Layer half of the flour tortillas on the bottom of the prepared baking dish.

Spread half of the meat mixture evenly over the tortillas.

Sprinkle half of the shredded Cheddar cheese over the meat mixture.

Repeat the layers with the remaining tortillas, meat mixture, and cheese.

Bake in the preheated oven for 20 to 30 minutes, or until the cheese is melted and bubbly and the lasagna is heated through.

Let stand for a few minutes before cutting and serving.