In a skillet, cook ground beef and chopped onions over medium heat until beef is browned and onions are soft. Drain any excess fat.
In a large mixing bowl, combine the cooked beef and onions, sliced potatoes, cream of mushroom soup, melted butter, salt, and black pepper.
Spread the mixture evenly in a 9x13 inch casserole dish.
Top with frozen mixed vegetables and cover with aluminum foil.
Bake in the preheated oven for 30 minutes. Remove the foil, add shredded cheddar cheese on top, and bake for an additional 15 minutes or until cheese is melted and bubbly.
Notes
Feel free to add any additional spices or herbs to taste. Serve hot.