Heat the oil in a 12-inch skillet over medium-high heat. Add the chicken and cook for 10 minutes or until well browned on all sides. Stir the garlic, Italian seasoning, tomatoes, mushrooms, onions, pepper and 1 cup broth in a 6-quart slow cooker. Add the chicken and turn to coat. Cover and cook on LOW for 7 to 8 hours or until the chicken is cooked through. Remove the chicken from the cooker, cover and keep warm. Stir the cornstarch and remaining broth in a small bowl until the mixture is smooth. Stir the cornstarch mixture in the cooker. Cover and cook on HIGH for 10 minutes or until the mixture boils and thickens. Serve with the chicken and pappardelle.
Serving Suggestion: This recipe is delicious sprinkled with shredded Parmesan cheese before serving.