Preheat the oven to 375°F (190°C).
Cook the jumbo pasta shells according to the package instructions until al dente. Drain and set aside to cool slightly.
In a skillet, heat the olive oil over medium heat. Add the shredded chicken and sauté for about 5 minutes until heated through.
In a mixing bowl, combine the ricotta cheese, ½ cup of mozzarella cheese, Parmesan cheese, cream cheese, Cajun seasoning, garlic powder, onion powder, salt, and black pepper. Mix until well combined.
Gently fold the sautéed chicken into the cheese mixture until evenly distributed.
Stuff each cooked pasta shell with the creamy chicken mixture and arrange them in a greased baking dish.
Pour the marinara sauce evenly over the stuffed shells. Sprinkle the remaining mozzarella cheese on top.
Cover the dish with aluminum foil and bake for 20 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Once done, remove from the oven and let it cool for a few minutes. Garnish with chopped green onions before serving.