Preheat the oven to 375°F (190°C).
Cook the pasta shells: Boil salted water and cook the pasta shells according to the package instructions. Drain and set aside.
Prepare the filling: In a large mixing bowl, combine the cooked chicken, chopped broccoli, ricotta cheese, mozzarella, Parmesan, egg, garlic powder, onion powder, salt, and pepper. Mix until well combined.
Stuff the shells: Carefully stuff each pasta shell with the chicken and broccoli mixture. Place them in a baking dish.
Prepare the baking dish: Spread a thin layer of marinara sauce at the bottom of the dish. Place the stuffed shells on top.
Top with sauce and cheese: Pour the remaining marinara sauce over the shells and sprinkle with the remaining mozzarella cheese.
Bake: Cover with foil and bake for 20 minutes. Then, remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Serve: Let the dish cool for a few minutes, then serve and enjoy!