01 - Preheat your oven to 400°F (200°C).
02 - Season chicken breasts with salt and black pepper on both sides.
03 - Heat olive oil in a large skillet over medium-high heat. Sear chicken breasts for 2–3 minutes per side until lightly golden. Transfer to a baking dish.
04 - In the same skillet, melt butter over medium heat. Add onions and cook for 2–3 minutes until translucent.
05 - Add garlic and mushrooms; sauté for 5–6 minutes until mushrooms are browned and their liquid has evaporated.
06 - Sprinkle flour over the mushroom mixture, stir, and cook for 1 minute.
07 - Gradually incorporate chicken broth, stirring constantly to achieve a smooth consistency. Add heavy cream, thyme, oregano, and Parmesan cheese. Stir until the sauce is smooth and slightly thickened, approximately 2–3 minutes. Adjust seasoning with salt and pepper as desired.
08 - Pour the creamy mushroom sauce evenly over the seared chicken breasts in the baking dish.
09 - Bake uncovered for 20–25 minutes, or until the internal temperature of the chicken reaches 165°F (74°C).
10 - Remove from the oven, sprinkle with chopped parsley, and serve immediately.