Heat olive oil in a large pot over medium heat. Add diced chicken breasts and season with salt and pepper. Sauté until the chicken is cooked through and nicely browned. Remove the chicken from the pot and set aside.

In the same pot, melt butter over medium heat. Add chopped onion and minced garlic. Sauté until the onion becomes translucent and fragrant, about 3-4 minutes.

Toss in the sliced cremini mushrooms and continue to cook until they are soft and golden brown, about 5-6 minutes.

Sprinkle flour over the mushroom mixture and stir to combine. Cook for 2-3 minutes to get rid of the raw flour taste.

Pour in the Marsala wine, scraping up any browned bits from the bottom of the pot. Let it simmer for a couple of minutes to reduce slightly and infuse the flavors.

Slowly pour in the chicken broth while stirring continuously. Add dried thyme and oregano. Bring the soup to a gentle simmer and let it cook for 10-15 minutes to allow the flavors to meld together.

Return the cooked chicken to the pot. Stir in heavy cream and let the soup simmer for an additional 5-10 minutes, or until it has thickened slightly.

Taste the soup and adjust the seasoning with salt and pepper according to your preference. Ladle the soup into bowls, garnish with freshly chopped parsley, and serve hot.