Season the chicken breasts with salt and pepper. Dredge each breast in flour, shaking off the excess.

In a large skillet, heat 2 tablespoons of olive oil over medium-high heat. Add the chicken breasts and cook for about 4-5 minutes on each side, or until golden brown and cooked through. Remove the chicken from the skillet and set aside.

In the same skillet, add the remaining 2 tablespoons of olive oil. Add the sliced mushrooms and sauté for about 5 minutes, or until they are browned and tender.

Pour in the Marsala wine, scraping the bottom of the skillet to deglaze. Allow the wine to simmer for about 2-3 minutes.

Add the chicken broth and return the chicken to the skillet. Simmer for an additional 5 minutes, allowing the flavors to meld.

Stir in the butter until melted and well combined. Adjust seasoning if necessary.

Serve the chicken topped with the mushroom sauce and garnish with fresh parsley.