Butterfly and pound chicken breasts. Using a sharp knife, slice the chicken breasts lengthwise down the center to create two thinly sliced breasts. Using a meat mallet, pound the chicken breasts for a few seconds. This helps you have tender chicken. Do NOT skip this step.
In a shallow bowl mix together flour, salt & pepper. Coat the chicken breasts in the flour mixture.
Prepare a greased 9x13 glass baking dish and preheat your oven to 300 degrees.
In a large pan on the stove, heat 1 tablespoon of olive oil. Sear the chicken for 6-7 minutes per side until golden brown. Once browned, place the chicken in the glass baking dish, cover, and put in the oven to keep warm.
In the same pot you sautéd the chicken, add the remaining 1 tablespoon of olive oil and heat. Add garlic, onion and mushrooms. Saute for 7-10 minutes until softened. Add the marsala wine & chicken broth, stirring to scrape up any browned bits on the bottom of the pan. Cook for an additional 2 minutes.
When the mushrooms are softened, remove the chicken from the oven and pour the broth/mushroom mixture on top of the chicken. You can bake in the oven for a few more minutes, or serve immediately. Top with fresh parsley & enjoy.