Preheat your oven to 350°F.
Boil the jumbo shells according to package directions until tender. Drain and set aside.
Cook the Italian sausage in a medium skillet over medium heat, breaking it apart until browned.
Pour enough pasta sauce to cover the bottom of a 9x13-inch casserole dish.
In a large bowl, combine the cooked sausage, ricotta, Parmesan, half of the mozzarella, Italian seasoning, garlic powder, salt, pepper, and 2 cups of the sauce.
Fill each pasta shell with the mixture and arrange them in the prepared casserole dish.
Pour the remaining sauce over the shells, then top with the remaining mozzarella cheese.
Cover the casserole with foil and bake for 30 minutes.
Remove the foil and bake for an additional 20–30 minutes, until the cheese is melted and bubbly. For extra golden cheese, broil for 2–3 minutes on high.
Sprinkle with fresh parsley before serving.