Preheat your oven to 375°F (190°C).
Cook the jumbo pasta shells in a large pot of boiling salted water according to package directions until al dente, then drain and set aside to cool.
In a small skillet over medium heat, wilt the fresh spinach with a splash of water for 1-2 minutes until soft.
Squeeze all excess moisture out of the wilted spinach using a clean kitchen towel and finely chop it.
In a medium mixing bowl, combine the ricotta cheese, chopped spinach, egg white, garlic powder, dried oregano, sea salt, and black pepper until well incorporated.
Spread half of the marinara sauce evenly across the bottom of a small baking dish.
Generously stuff each cooked pasta shell with the spinach and ricotta mixture and arrange them in the baking dish.
Top the shells with the remaining marinara sauce, shredded mozzarella, and parmesan cheese.
Cover the dish with foil and bake for 20 minutes, then remove the foil and bake for another 5-10 minutes until the cheese is melted and slightly golden.