Preheat your oven to 375°F (190°C).
Bring a large pot of salted water to a boil and cook the jumbo shells according to package directions until al dente, then drain and set aside.
In a non-stick skillet over medium heat, brown the ground turkey until fully cooked through, breaking it into small crumbles.
Add the fresh baby spinach to the skillet with the turkey and sauté for 1-2 minutes until just wilted, then remove from heat to cool slightly.
In a medium mixing bowl, combine the cooked turkey, wilted spinach, ricotta cheese, egg whites, garlic powder, dried oregano, sea salt, and black pepper.
Spread half of the marinara sauce in the bottom of a small baking dish.
Generously stuff each cooked pasta shell with the turkey and ricotta mixture and place them in the baking dish.
Top the shells with the remaining marinara sauce, shredded mozzarella, and grated parmesan.
Cover the dish with foil and bake for 15 minutes, then remove the foil and bake for an additional 5-10 minutes until the cheese is melted and bubbling.