Preheat oven to 350 degrees F. In a medium skillet over medium high heat, cook the ground beef and onion until beef is evenly browned and onion is tender.

Prepare the enchilada sauce according to package directions. Pour 1/4 cup of the sauce into the bottom of a 9x13 inch baking dish.
Pour the remaining sauce over the top of the enchiladas and sprinkle with the remaining cheese.

Bake in a preheated oven for 20 minutes, or until the sauce is bubbly and cheese is thoroughly melted.