Preheat the oven to 375°F (190°C).
Lightly grease a 9x13-inch baking dish.
Season the chicken breasts with salt, pepper, and garlic powder.
Heat the olive oil in a large skillet over medium-high heat.
Sear the chicken for 2 to 3 minutes per side until lightly golden. Remove and set aside.
In the same skillet, cook the mushrooms until softened and lightly browned.
Add the onion and cook for 3 minutes.
Stir in the garlic and cook for 30 seconds.
Add the cream of mushroom soup, heavy cream, chicken broth, thyme, and Parmesan cheese.
Stir until smooth and heated through.
Transfer the chicken to the prepared baking dish.
Pour the mushroom sauce evenly over the chicken.
Cover loosely with foil.
Bake for 25 minutes.
Remove the foil and continue baking for 15 to 20 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).
Let rest for 5 minutes before serving.
Garnish with fresh parsley.