Preheat your oven to 375°F (190°C).
Cook the jumbo pasta shells in a large pot of boiling salted water for 2 minutes less than the package instructions until al dente, then drain and set aside.
In a medium skillet over medium heat, cook the ground turkey with the minced garlic until the meat is fully browned and cooked through.
In a medium mixing bowl, stir together the cooked turkey, ricotta cheese, chopped fresh spinach, egg, sea salt, black pepper, and dried oregano until well combined.
Spread half of the marinara sauce into the bottom of a small baking dish.
Stuff each cooked pasta shell generously with the turkey and ricotta mixture and arrange them in the baking dish.
Pour the remaining marinara sauce over the shells and sprinkle evenly with the shredded mozzarella cheese.
Cover the dish with foil and bake for 20 minutes, then remove the foil and bake for an additional 10 minutes until the cheese is melted and bubbling.