• Step 1: Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish with non-stick cooking spray or butter.
• Step 2: Bring a large pot of salted water to a boil. Cook the manicotti shells according to the package instructions, about 8-10 minutes, until al dente. Drain and set aside to cool slightly.
• Step 3: In a medium bowl, combine the ricotta cheese, 1 cup of mozzarella cheese, Parmesan cheese, egg, parsley, garlic powder, salt, and black pepper. Mix well until fully incorporated.
• Step 4: Using a spoon or piping bag, carefully fill each manicotti shell with the cheese mixture, distributing it evenly.
• Step 5: Spread half of the marinara sauce in the prepared baking dish. Arrange the stuffed manicotti shells in a single layer. Pour the remaining marinara sauce over the top and sprinkle with the additional mozzarella cheese.
• Step 6: Bake for 25-30 minutes, or until the cheese is melted and bubbly. Let the dish sit for 5 minutes before serving.