01 - Sprinkle salt and black pepper evenly over both sides of the chicken breasts.
02 - Heat olive oil in a large skillet over medium-high heat. Add chicken and cook 5 to 6 minutes per side until golden brown and cooked through. Remove and keep warm covered loosely with foil.
03 - In the same skillet, add sliced mushrooms and chopped onion. Cook, stirring occasionally, for 4 to 5 minutes until mushrooms are golden and onions are translucent.
04 - Stir in minced garlic and thyme leaves. Sauté for 1 minute until fragrant.
05 - Pour in chicken stock and scrape browned bits from the skillet’s bottom. Simmer for 2 minutes to reduce slightly.
06 - Reduce heat to medium. Stir in heavy cream, Parmesan cheese, and Dijon mustard. Simmer gently for 3 to 4 minutes until the sauce thickens.
07 - Place chicken back in the skillet, spoon sauce over the top, and simmer for another 2 to 3 minutes until heated through.
08 - Sprinkle chopped parsley over the dish and serve immediately while hot.