Preheat and prep. Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with cooking spray.
Mix the casserole. In a large bowl, combine the frozen hash browns, condensed cream of potato soup, sour cream, shredded Cheddar cheese, and diced ham. Mix until everything is well combined and evenly distributed.
Transfer to baking dish. Spread the mixture evenly into the prepared 9x13-inch baking dish. Use a spatula to smooth the top.
Top with Parmesan. Sprinkle the grated Parmesan cheese evenly over the top of the casserole.
Bake until golden. Bake in the preheated oven for about 1 hour, until the casserole is bubbly around the edges and lightly golden brown on top.
Rest and serve. Let the casserole rest for 5-10 minutes before serving. This helps it set up and makes it easier to cut into portions. Serve warm and enjoy!