Preheat your oven to 375°F (190°C).
Grease a 9x13-inch baking dish or line with a spoonful of marinara to coat the bottom. This helps prevent the shells from sticking and adds moisture.
Cook the pasta shells.
Bring a large pot of salted water to a boil. Add the jumbo shells and cook until just al dente (usually 1–2 minutes less than the box recommends). Drain and set aside to cool slightly so they’re easier to handle.
Prepare the cheese filling.
In a large bowl, mix together the ricotta, 1 ½ cups mozzarella, parmesan, garlic powder, parsley, black pepper, and a pinch of salt. Stir until creamy and well combined.
Fill the shells.
Spoon the cheese filling into each shell, about 1 to 2 tablespoons per shell depending on size. Nestle the filled shells into your baking dish on top of the sauce.
Add more sauce and cheese.
Pour the remaining marinara sauce over the top of the stuffed shells, covering them generously. Sprinkle a handful of shredded mozzarella on top for a bubbly, cheesy finish.
Bake until golden and bubbly.
Cover loosely with foil and bake for 20 minutes. Remove the foil and bake for another 10–15 minutes, or until the cheese is melted and lightly golden around the edges.
Let cool slightly and serve.
Let the dish rest for about 5 minutes before serving. Pair with warm bread, a salad, or roasted vegetables for a cozy and complete dinner.