Preheat oven to 375F.
Drop the ground beef into a large skillet over medium-high heat and break it apart.
Add the diced onions to the skillet. Stir well and continue cooking until the ground beef is fully browned.
Spray a 9 x 13 inch baking dish well with cooking spray.
Pour the frozen pierogies into the baking dish and spread them out evenly.
Pour 1 can of the red enchilada sauce over the pierogies.
Spoon the cooked ground beef and onions over the pierogies.
Sprinkle 1 cup of the shredded cheddar over top.
Pour the remaining can of enchilada sauce over everything.
Sprinkle the remaining 2 cups of shredded cheddar cheese over top.
Cover the dish with aluminum foil.
Place the dish in the oven and bake for 40 minutes. Remove the foil and continue baking for 5 - 10 minutes uncovered to finish melting the cheese.
Remove the dish from the oven and allow it to rest for 5 minutes to allow the sauce to thicken up.
Serve and enjoy!
