Preheat the oven to 350°F (175°C) and lightly grease a 9x13 inch baking dish with cooking spray or butter.
In a mixing bowl, combine the cream of chicken soup, sour cream, garlic powder, onion powder, salt, and pepper. Mix well until all ingredients are fully combined.
Spread the uncooked rice evenly over the bottom of the prepared baking dish.
Place the chicken breasts on top of the rice in a single layer.
Pour the soup mixture over the chicken breasts and rice, ensuring everything is well covered. If using, add diced bell pepper and mushrooms on top.
Pour the chicken broth evenly over the mixture in the baking dish.
Cover the dish tightly with aluminum foil and bake in the preheated oven for 30 minutes.
After 30 minutes, remove the foil and sprinkle the shredded cheddar cheese on top.
Return the dish to the oven uncovered and bake for an additional 15 minutes or until the chicken is cooked through and the cheese is melted and bubbly.
Once done, remove from the oven and let it sit for about 5 minutes before serving. Garnish with fresh parsley if desired.