Cook the Pasta: Bring a large pot of salted water to a boil. Add the jumbo shells and cook according to the package instructions, usually about 9-11 minutes, until al dente. Drain the shells and set them aside to cool slightly.

Prepare the Filling: In a medium mixing bowl, combine the ricotta cheese, 1 cup of mozzarella cheese, Parmesan cheese, egg, basil, garlic powder, oregano, salt, and pepper. Stir until all ingredients are well mixed.

Stuff the Shells: Once the shells are cool enough to handle, spoon about 2 tablespoons of the ricotta mixture into each shell. Gently press the filling into the shell and place it in a greased 9×13-inch baking dish. Repeat until all shells are filled.

Assemble the Dish: Pour half of the marinara sauce evenly over the stuffed shells. Sprinkle the remaining 1/2 cup of mozzarella cheese over the top.

Bake: Cover the baking dish with aluminum foil and bake in a preheated oven at 375°F (190°C) for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the cheese is melted and bubbly.

Serve: Let the stuffed shells cool for a few minutes before serving. Garnish with fresh parsley, if desired. Serve with extra marinara sauce or a side salad.