Preheat oven to 350°F (175°C).
Add rice to a 9x13 baking dish. Pour in chicken broth.
Sprinkle the onion soup mix over rice, then add diced onion, mushrooms, and veggies.
Pour melted butter over everything and mix well.
Season chicken with salt and pepper. Place on top of rice mixture.
Cover tightly with foil and bake for 2 hours.
Optional: Uncover and bake an additional 15 minutes to crisp up the chicken skin.
Let rest 5–10 minutes before serving. Enjoy!