Preheat oven to 375°F (190°C). Grease a baking dish with cooking spray.
Cook jumbo shells according to package instructions. Drain and set aside.
In a large bowl, mix ricotta, mozzarella, Parmesan, cream cheese, egg, Italian seasoning, garlic powder, salt, and pepper.
Fill each cooked shell with the cheese mixture and place them in the baking dish.
Pour marinara sauce over the stuffed shells, ensuring they are evenly coated.
Sprinkle additional mozzarella cheese on top.
Cover with foil and bake for 25 minutes.
Remove foil and bake for another 10 minutes, until cheese is bubbly and slightly golden.
Let cool for 5-10 minutes, then garnish with fresh parsley and serve.