Preheat your oven to 350°F (175°C).
Cook the jumbo pasta shells according to the package instructions until al dente. Drain and set aside.
In a large mixing bowl, combine the shredded chicken, steamed broccoli, ricotta cheese, half of the mozzarella cheese, garlic powder, salt, and pepper. Mix well until everything is combined.
Take each cooked pasta shell and fill it with the chicken and broccoli mixture. Place the stuffed shells in a greased baking dish.
Pour the Alfredo sauce over the stuffed shells, ensuring they are well-coated. Sprinkle the remaining mozzarella cheese and grated Parmesan cheese on top.
Cover the baking dish with aluminum foil and bake in the preheated oven for 20 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and slightly golden.
Once baked, remove from the oven and let it cool for a few minutes. Garnish with chopped fresh parsley before serving.