Preheat your oven to 375°F (190°C).
Cook the jumbo pasta shells in a large pot of boiling water until al dente, then drain and set aside to cool.
Heat the olive oil in a skillet over medium heat and sauté the minced garlic for about 30 seconds until fragrant.
Add the ground turkey to the skillet, breaking it apart with a spatula, and cook until fully browned.
Stir in the chopped baby spinach and cook for 1-2 minutes until just wilted, then remove from heat.
In a medium mixing bowl, combine the ricotta cheese, egg white, turkey-spinach mixture, sea salt, black pepper, and dried oregano.
Spread half of the marinara sauce across the bottom of a small oven-safe baking dish.
Stuff each cooked shell generously with the turkey and ricotta mixture, then arrange them in the baking dish.
Top the shells with the remaining marinara sauce and sprinkle the mozzarella cheese evenly over the top.
Cover the dish with foil and bake for 20 minutes, then remove the foil and bake for an additional 5 minutes until the cheese is bubbly and golden.