Preheat your oven to 350°F (175°C).
In a large skillet, brown the ground beef and chopped onions over medium heat until the beef is no longer pink and the onions are translucent.
Add the cream of mushroom soup, egg noodles, and mixed vegetables to the skillet, stirring to combine thoroughly.
Season with salt and pepper, mixing well, and allow the mixture to simmer for 5 minutes.
Transfer the mixture into a greased 9x13 baking dish, spreading it evenly.
Sprinkle the shredded cheddar cheese on top of the mixture evenly.
Cover the dish with aluminum foil and bake for 25 minutes.
After 25 minutes, remove the foil and continue baking for another 15 minutes, or until the cheese is bubbly and golden brown.
Let the casserole cool for a few minutes before serving.