Preheat your oven to 375°F (190°C).
Cook the jumbo pasta shells in a pot of boiling water according to package directions until al dente, then drain and set aside to cool slightly.
In a medium skillet over medium-high heat, add the olive oil and the ground turkey.
Sauté the turkey, breaking it into small crumbles with a wooden spoon, until browned and cooked through.
Stir in the garlic powder, dried oregano, sea salt, and black pepper to season the meat.
Add the fresh baby spinach to the skillet and cook for 1-2 minutes until completely wilted, then remove the pan from the heat.
In a small mixing bowl, combine the cooked turkey and spinach mixture with the ricotta cheese until well incorporated.
Spread a thin layer of marinara sauce (about 2 tablespoons) onto the bottom of a small oven-safe baking dish.
Generously stuff each cooked pasta shell with 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.
Bake for 15-20 minutes until the sauce is bubbling and the cheese has melted into a golden crust.