01 - Pat chicken breasts dry with paper towels. Season both sides generously with salt and pepper, pressing gently to help the seasoning adhere.
02 - Heat olive oil in a large skillet over medium-high heat until shimmering. Add chicken breasts and sear for 3 to 4 minutes per side until golden brown and cooked through. Transfer to a plate and cover loosely with aluminum foil to rest.
03 - Reduce heat to medium. Add butter to the same skillet and swirl to coat. Add sliced mushrooms and sauté for 5 to 6 minutes, stirring occasionally, until browned and their liquid has evaporated.
04 - Stir in minced garlic and cook for 1 minute until fragrant, being careful not to burn it.
05 - Pour in heavy cream, chicken broth, and Dijon mustard. Add fresh thyme leaves and dried oregano. Stir well to combine and bring to a gentle simmer. Cook for 3 to 4 minutes, stirring occasionally, until the sauce thickens slightly.
06 - Return chicken to the skillet, nestling pieces into the sauce. Simmer for 2 to 3 minutes until chicken is heated through and well-coated. Stir in chopped parsley. Taste and adjust seasoning with additional salt and pepper if needed.
07 - Transfer chicken to serving plates, spooning mushrooms and sauce generously over the top. Garnish with extra fresh parsley if desired. Serve immediately alongside mashed potatoes, rice, or pasta.