Divide the chicken breasts horizontally to yield four uniform cutlets, then place each piece between plastic wrap and gently pound until approximately 1/3-inch thick. Season all sides with salt and pepper, dredge lightly in flour, shaking off any excess, and set aside. Heat a broad, heavy skillet over medium heat, adding olive oil and butter. Once the oil and butter are shimmering, introduce the floured chicken cutlets and sauté until both sides are golden and the interior reaches 165˚F, about 3–4 minutes per side. Transfer the cooked chicken to a plate and cover loosely with foil to retain warmth. If necessary, add a touch more oil to the pan and add the mushrooms. Cook until their moisture evaporates and they acquire a rich golden hue, about 5 minutes. Stir in onion powder and minced garlic, sautéing for an additional 30 seconds until aromatic. Pour in the Marsala wine, scraping up any browned bits from the pan, then raise the heat and reduce the wine by about half, approximately 4–5 minutes. Add the chicken stock and gradually stream in the heavy cream while stirring. Reduce the heat to maintain a gentle simmer and allow the sauce to cook for another 4–5 minutes, or until it thickens slightly. Taste and adjust the seasoning with salt as needed. Return the chicken to the skillet, scatter chopped parsley over the top, and spoon the sauce generously over the cutlets. Let everything heat through for an additional 2 minutes, allowing the sauce to reach your preferred consistency, bearing in mind it will continue to thicken slightly upon standing.