Begin by seasoning the chicken breasts with salt and black pepper. Dredge each breast in flour, shaking off any excess.
In a large skillet, heat 2 tablespoons of olive oil over medium-high heat. Once hot, 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, until they are browned and tender. Stir in the minced garlic and cook for an additional minute.
Pour in the Marsala wine, scraping the bottom of the skillet to deglaze. Allow the wine to simmer for about 2-3 minutes, reducing slightly.
Add the chicken broth and return the chicken to the skillet. Simmer for another 5 minutes, allowing the flavors to meld.
Stir in the butter until melted and well combined. Adjust seasoning with salt and pepper if needed.
Serve the chicken hot, garnished with fresh parsley.