- Preheat oven to 350°F and grease 9 x 13 baking dish with nonstick cooking spray.
- Combine ricotta, spinach, mushrooms and Parmesan together in large bowl. Spoon ricotta mixture into shells.
- Spread 1 cup marinara sauce evenly over bottom of prepared baking dish. Place stuffed shells, filled side up, on top of sauce. Spread remaining marinara sauce over shells and top with chicken. Cover baking dish with aluminum foil and bake for 15 minutes. Remove foil and sprinkle with mozzarella cheese. Bake for an additional 5 minutes until the cheese is melted. Top with parsley and serve.
Tip: Pre-sliced mushrooms can usually be found in the produce aisle of your local grocer.