Preheat your oven to 375°F (190°C).
Cook the jumbo pasta shells in a pot of boiling salted water until al dente, then drain and set aside to cool.
In a small non-stick skillet over medium heat, brown the ground turkey until fully cooked and crumbly.
Steam the fresh baby spinach until wilted, then squeeze out all excess moisture and chop the leaves finely.
In a medium mixing bowl, combine the ricotta cheese, egg white, chopped spinach, parmesan cheese, garlic powder, oregano, sea salt, and black pepper.
Stir the cooked ground turkey into the marinara sauce to create a high-protein meat sauce.
Spread roughly half of the meat sauce into the bottom of a small oven-safe baking dish.
Generously stuff each cooked pasta shell with the ricotta and spinach mixture and arrange them in the baking dish.
Spoon the remaining meat sauce over the shells and sprinkle evenly with the shredded mozzarella cheese.
Bake for 20 minutes, or until the sauce is bubbling and the mozzarella has melted into a golden crust.