Preheat the oven to 375°F (190°C). Lightly spray a 9x13-inch baking dish with nonstick cooking spray.
Season both sides of the chicken breasts with garlic powder, onion powder, salt, and pepper. Arrange them in a single layer in the baking dish.
Evenly distribute the uncooked rice over and around the chicken.
In a mixing bowl, whisk together chicken broth, sour cream, and shredded cheddar cheese until smooth.
Pour the mixture evenly over the chicken and rice, ensuring everything is covered.
Seal the baking dish tightly with foil to trap steam. Bake for 40–45 minutes.
Remove the foil and bake for another 10–15 minutes until the top is golden and bubbly.
Let the casserole cool for 5–10 minutes before serving. The sauce will thicken slightly as it cools.