Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking dish.

Season the chicken breasts with salt and pepper. In a large skillet, melt the butter over medium heat and cook the chicken until golden brown on both sides (about 4-5 minutes per side). Remove and set aside.

In the same skillet, sauté the diced onion and mushrooms until softened (about 5 minutes). Add the minced garlic and cook for another minute.

In your prepared baking dish, combine the uncooked rice, sautéed vegetables, cream of chicken soup, chicken broth, heavy cream, thyme, and remaining salt and pepper. Stir well to combine.

Place the browned chicken breasts on top of the rice mixture.

Cover tightly with aluminum foil and bake for 45 minutes.

Remove the foil, sprinkle with shredded cheese, and bake uncovered for an additional 10-15 minutes, until the cheese is melted and bubbly.

Let rest for 5-10 minutes before serving to allow the sauce to thicken.