Preheat your oven to 375°F (190°C).
Cook the jumbo pasta shells according to package instructions until al dente. Drain and set aside to cool slightly.
In a large bowl, combine the shredded turkey, ricotta cheese, half of the mozzarella cheese, Parmesan cheese, garlic powder, Italian seasoning, salt, and pepper. Mix until well combined.
Spread half of the marinara sauce on the bottom of a 9x13 inch baking dish.
Stuff each cooked pasta shell with the turkey mixture and place them in the baking dish, open side up.
Pour the remaining marinara sauce over the stuffed shells and sprinkle the remaining mozzarella cheese on top.
Cover the dish with aluminum foil and bake for 25 minutes. Then, remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Remove from the oven and let cool for a few minutes. Garnish with fresh parsley before serving.