Place olive oil in the bottom of your slow cooker followed by the chicken, onion, butter, garlic, mushrooms, white wine, and chicken broth.
Cook on high for 4 hours or low for 6 hours.
Remove about 1/8 cup of liquid from the slow cooker and stir it into the flour to make a roux.
Add shredded mozzarella cheese and roux to the slow cooker and stir to mix.
Allow chicken marsala to continue to cook for about 10 minutes or until the cheese is fully melted.
Serve over noodles of any kind with some additional parmesan cheese for garnish!