Preheat your oven to 400°F (200°C) to ensure a crispy, golden casserole.
In a large skillet, cook the ground beef and diced onion over medium heat until the meat is browned and the onions are soft. Drain any excess fat, then season with salt and pepper.
Add the cheddar cheese soup, garlic powder, and paprika to the skillet. Stir until smooth and creamy, then remove from heat.
Grease a 9x13-inch baking dish. Spread half of the frozen French fries evenly in the bottom.
Spoon the beef mixture evenly over the fries. Sprinkle half of the shredded cheddar and mozzarella cheese on top of the beef.
Add the remaining fries, then top with the rest of the cheese.
Bake uncovered for 25-30 minutes, until the cheese is melted and bubbly, and the top is golden brown.
Let the casserole cool for a few minutes before serving. Optionally, drizzle with burger sauce or ketchup.