Add the chicken breast to the bottom of the slow cooker along with the sliced mushrooms and onions
Season the chicken breast, onions and mushrooms with salt, pepper and garlic.
Pour in the chicken broth and wine into the slow cooker over the chicken and mushrooms.
Place the lid on the slow cooker and cook on low for 4-5 hours. The chicken should read an internal temperature of 165 F.
Spoon out about 1/4 cup of liquid and whisk with the corn starch. Pour back into the slow cooker for cook for another 15 minutes to allow the liquid to thicken. Add more broth if a thinner sauce is desired.
Remove the lid and top with the cooked chicken marsala with fresh parsley.
Enjoy! Serve with a pasta of your choice like zucchini noodles, spaghetti squash, chickpea pasta or whole wheat pasta.