Preheat your oven to 350°F (175°C).
Lightly grease a 9×13-inch baking dish to prevent sticking.
Season both sides of the chicken breasts with salt and pepper.
Arrange them neatly in the prepared baking dish.
In a mixing bowl, whisk together the cheddar cheese soup, milk, sour cream, and garlic powder until smooth and well-blended.
Pour half of this mixture over the chicken.
Scatter the broccoli florets across the layer of soup mixture.
Ensure they are evenly distributed for balanced flavor.
Sprinkle the shredded cheddar and Parmesan cheese over the broccoli and chicken.
Pour the remaining soup mixture over everything.
Bake in the preheated oven for 45-50 minutes or until the chicken is cooked through and the casserole is bubbly.