Fill a large pot with water, add a pinch of salt, and bring it to a boil. Gently add the jumbo shells and cook according to the package instructions until al dente, usually around 10-12 minutes. Stir occasionally to prevent sticking. Once cooked, drain the shells in a colander and drizzle with 1 tablespoon olive oil to keep them from sticking together. Set aside to cool slightly.
In a large mixing bowl, combine 2 cups ricotta cheese, 1 cup chopped fresh spinach, 1 cup shredded mozzarella, 1/2 cup grated parmesan, and 1 egg. Season with 1 teaspoon garlic powder, 1 teaspoon onion powder, salt, and pepper to taste. Mix everything thoroughly until well combined. The egg helps bind the filling so it stays inside the shells during baking.
Take each cooked pasta shell and gently fill it with the ricotta-spinach mixture using a spoon or small spatula. Fill each shell generously but carefully to avoid tearing the pasta. Place the stuffed shells open side up in a lightly greased 9x13-inch baking dish.
Pour 2 cups of marinara sauce evenly over the arranged stuffed shells. This sauce adds moisture and flavor as the shells bake. For an extra creamy twist, feel free to add a drizzle of Alfredo Sauce mixed with the marinara for a rich, velvety finish.
Cover the baking dish tightly with aluminum foil and bake in a preheated oven at 375°F (190°C) for 25 minutes. Afterward, remove the foil and bake for an additional 10 minutes to allow the cheese on top to turn golden and bubbly. Let the dish rest for 5 minutes before serving.