Boil the jumbo pasta shells in salted water until al dente, then drain and let them cool slightly.
In a mixing bowl, combine ricotta, shredded mozzarella, grated Parmesan, cream cheese, chopped parsley, garlic powder, salt, and black pepper until well mixed.
Generously fill each pasta shell with the cheese mixture.
Spread marinara sauce evenly in the bottom of a baking dish.
Place the stuffed shells on top of the marinara sauce, then spoon more sauce over them and sprinkle with additional shredded mozzarella.
Bake in a preheated oven at 375°F (190°C) for 15 to 18 minutes, until the dish is bubbly and the cheese is melted.
Garnish with chopped parsley and serve warm.