Preheat the oven to 375°F (190°C) and grease a 9x13 inch baking dish with non-stick spray.
In a large skillet over medium-high heat, brown the ground beef until cooked through; drain the excess fat thoroughly.
Season the cooked beef with garlic powder, onion powder, smoked paprika, salt, and black pepper, stirring to combine.
In a small mixing bowl, whisk together the condensed cream of mushroom soup and milk until the mixture is uniform.
Arrange half of the potato slices in the bottom of the prepared baking dish, followed by a layer of diced onions.
Spread the seasoned ground beef evenly over the onion layer, then top with the remaining potato slices.
Pour the soup and milk mixture evenly over the top layer of potatoes.
Cover the dish tightly with aluminum foil and bake for 45 minutes.
Remove the foil, sprinkle the shredded cheddar cheese over the top, and return to the oven for 15 minutes or until the potatoes are tender and the cheese is melted and bubbly.