Bring a large pot of salted water to a boil. Add the 12 jumbo pasta shells and cook according to the package instructions until al dente—usually about 9 to 11 minutes. Drain carefully and rinse with cold water to stop the cooking process. Set aside on a plate lightly drizzled with olive oil to prevent sticking.
In a large bowl, combine 2 cups chopped fresh spinach, 1 cup ricotta cheese, 1/2 cup crumbled feta cheese, and 1/2 cup grated parmesan cheese. Add 1 beaten egg, 1 teaspoon garlic powder, 1 teaspoon onion powder, and season with salt and pepper to taste. Mix everything together until evenly combined and creamy.
Using a spoon or small scoop, carefully fill each cooked shell with the spinach and cheese mixture. Be generous but avoid overfilling to keep the shells intact.
Preheat your oven to 375°F (190°C). Spread 1 cup of marinara sauce evenly on the bottom of the baking dish. Arrange the stuffed shells in a single layer on top of the sauce. Pour the remaining 1 cup marinara sauce over the filled shells. Sprinkle 1 cup shredded mozzarella cheese evenly over the entire dish. Finally, sprinkle dried oregano and basil across the top for added aroma.
Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 10 minutes or until the cheese is bubbly and golden brown. Let the dish cool for 5 minutes before serving.
