Preheat your oven to 375°F (190°C).
Cook the jumbo pasta shells in a large pot of boiling salted water until al dente, then drain and set aside to cool.
In a medium skillet over medium-high heat, cook the ground turkey until browned and fully cooked, breaking it into small crumbles.
Add the fresh baby spinach to the skillet with the turkey and sauté for 1 minute until just wilted, then remove from heat.
In a medium bowl, stir together the ricotta cheese, egg white, grated parmesan, garlic powder, dried oregano, sea salt, and black pepper.
Fold the cooked turkey and wilted spinach into the ricotta mixture until thoroughly combined.
Spread half of the marinara sauce across the bottom of a small oven-safe baking dish.
Fill each cooked pasta shell with a generous amount of the turkey and ricotta mixture and arrange them in the baking dish.
Spoon the remaining marinara sauce over the shells and sprinkle evenly with the shredded mozzarella cheese.
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 the sauce is bubbling.