Thinly slice the chicken and dredge each piece lightly in flour. Set aside.

In a saucepan over high heat, combine the Marsala wine, cornstarch, and porcini mushrooms. Bring to a boil, then reduce the heat to medium-high and simmer until the liquid is reduced by half.

Meanwhile, heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Add the chicken and cook until golden brown on both sides. Remove from the skillet and set aside.

Once the wine mixture has reduced, strain it through a sieve, pressing on the mushrooms to extract as much liquid as possible. Discard the mushrooms and reserve the strained liquid in a bowl.

In the same skillet, heat 2 tablespoons of olive oil. Add the cremini mushrooms and cook until all water is cooked out of mushrooms. Transfer them to a bowl and set aside.

Add another tablespoon of olive oil to the skillet along with the shallot. Cook until softened. Stir in the tomato paste and garlic, and cook until fragrant.

Pour the reserved Marsala mixture into the skillet. Add lemon juice and oregano, and bring to a simmer.

Return the chicken to the skillet and simmer for 1–2 minutes per side, until heated through.

Remove the chicken and place it on a serving dish.

Whisk butter into the sauce until melted and slightly thickened. Stir in the parsley and cooked cremini mushrooms.

Spoon the sauce over the chicken and serve immediately.