**Preheat the Oven:** Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
**Cook the Kielbasa:** Heat a large skillet over medium heat. Add the sliced kielbasa and cook until browned on both sides, about 3-4 minutes. Remove from heat and set aside.
**Mix the Sauce:** In a large mixing bowl, combine the cream of chicken soup, sour cream, milk, garlic powder, onion powder, salt, and pepper. Stir until well blended.
**Assemble the Casserole:** Add the hash brown potatoes, browned kielbasa, and 1 cup of cheddar cheese to the bowl. Mix until evenly coated with the sauce.
**Transfer to Baking Dish:** Pour the mixture into the prepared baking dish and spread it out evenly.
**Add Toppings:** Sprinkle the remaining cheddar cheese, Parmesan cheese, and crushed crackers (if using) over the top.
**Bake:** Cover the dish with aluminum foil and bake for 30 minutes. Remove the foil and bake for an additional 15-20 minutes, or until the casserole is bubbly and the top is golden brown.
**Garnish and Serve:** Let the casserole rest for 5 minutes before garnishing with parsley and serving.