Preheat your oven to 350°F (175°C).
In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until softened, about 5 minutes.
Add the ground beef to the skillet and cook until browned. Drain any excess fat.
Stir in the mixed vegetables, garlic powder, salt, and black pepper. Cook for an additional 3-4 minutes, allowing the vegetables to warm through.
In a 9x13-inch baking dish, layer half of the sliced potatoes on the bottom.
Spoon half of the beef and vegetable mixture over the potatoes.
Spread half of the cream of mushroom soup over the beef mixture, followed by half of the shredded cheddar cheese.
Repeat the layers with the remaining potatoes, beef mixture, cream of mushroom soup, and cheese.
Cover the dish tightly with aluminum foil and bake in the preheated oven for 45 minutes.
After 45 minutes, remove the foil and bake for an additional 15 minutes, or until the potatoes are tender and the cheese is bubbly and golden.
Allow the casserole to cool for a few minutes before serving.