Gently pat the chicken cutlets dry with paper towels. If they are too thick, slide the chicken between two pieces of parchment and pound with a rolling pin until evenly then remove parchment. Next, season generously with salt and pepper on both sides.
Place the 1/3 cup flour in a zip-top bag, then add the chicken and shake to coat the cutlets completely. Remove the floured chicken from the bag, shaking off any excess flour and set cutlets aside on a piece of parchment paper.
Heat a large nonstick skillet over medium-high heat. Add 1 tablespoon of butter and 2 teaspoons of olive oil to the pan and swirl to melt the butter.
Add the chicken to the hot skillet and cook until nicely browned, about 3 minutes per side. Remove the chicken from the pan and set aside on a clean plate.
Add the remaining 1 teaspoon olive oil to the skillet and add the shallots and garlic. Sauté for about 30 seconds, until it’s fragrant.
Add the mushrooms to the skillet, and season with salt, pepper, and onion powder. Cook, stirring occasionally, until golden brown, about 6-8 minutes.
Sprinkle the remaining 1 teaspoon of flour over the mushrooms, and cook, stirring constantly, for about 30 seconds.
Pour in the Marsala wine and chicken stock, scraping up any browned bits from the bottom of the pan with a wooden spoon.
Simmer the sauce, stirring occasionally, until it thickens slightly, about 2 minutes.
Stir in the remaining 1 tablespoon of butter until melted and incorporated.
Return the chicken to the skillet with the mushrooms.
Reduce heat to low, cover with a lid, and simmer gently for 4-5 minutes to allow the flavors to meld.
Serve the chicken and mushrooms over the prepared pasta, then garnish with fresh parsley, and enjoy.