Begin by preheating your oven to 350°F (175°C) to ensure it's hot and ready for the casserole.
In a large mixing bowl, whisk together both cans of cream of chicken soup and cream of mushroom soup with the chicken broth. Add in the garlic powder, onion powder, dried thyme, and a pinch of salt and pepper. Mix until the mixture is smooth and well combined.
Grease a spacious 9x13 inch casserole dish with a bit of oil or cooking spray to prevent sticking. Spread the uncooked long-grain rice evenly along the bottom of the dish, forming a neat layer.
Pour the creamy soup mixture over the rice, using a spatula to gently spread it out and ensure the rice is fully covered by the liquid.
Arrange the chicken breasts on top of the soup mixture. Season them generously with additional salt, pepper, and a sprinkle of thyme to enhance their flavor.
Scatter the frozen mixed vegetables around the chicken breasts in the casserole dish, allowing them to distribute evenly throughout the dish.
Take a piece of aluminum foil and tightly cover the casserole, making sure it seals well around the edges to lock in moisture during baking.
Place the covered dish in the preheated oven and bake for 1 hour, allowing the flavors to meld and the rice to cook.
After 1 hour, carefully remove the foil, ensuring to avoid any steam burns, and evenly sprinkle the shredded cheddar cheese over the top of the casserole.
Return the dish to the oven, now uncovered, and bake for an additional 15-20 minutes. This will melt the cheese and create a delightful, bubbly crust.
Once the cheese is melted and the casserole is bubbly, carefully remove it from the oven. Let it sit for 10 minutes before serving; this resting time will help the casserole set and make it easier to serve.
Notes
Serve warm, garnished with fresh herbs for added flavor.