Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish.
Cut the chicken breasts into bite-sized pieces and halve the baby potatoes.
Chop the broccoli florets into small pieces.
You can sear the chicken cubes before adding them to the dish for extra flavor, but this step is optional.
In a large mixing bowl, whisk together the sour cream, cream of chicken soup, water, salt, and black pepper until well combined.
Add the chicken, potatoes, and broccoli to the bowl and toss to coat evenly.
Transfer the mixture to the greased baking dish and spread it out evenly.
Cover the dish with aluminum foil and bake for 30 minutes.
Remove the foil, sprinkle shredded cheddar cheese evenly over the top, and bake uncovered for another 15 minutes, or until the cheese is melted and bubbly.
Let the casserole rest for 5 minutes, then garnish with fresh parsley and serve warm!