In a large pot, bring salted water to a rolling boil. Carefully add the jumbo pasta shells and cook them according to the package instructions until they are al dente. After cooking, drain the pasta in a colander and allow them to cool for a few minutes.
In a spacious mixing bowl, combine the shredded chicken, buffalo sauce, softened cream cheese, ranch dressing, half of the shredded mozzarella cheese, and blue cheese crumbles if you choose to include them. Mix all the ingredients together until well incorporated. Adjust with salt and pepper as desired.
Lightly grease a 9x13-inch baking dish with cooking spray or a drizzle of oil.
Take each cooked pasta shell and carefully stuff it with the buffalo chicken mixture. Arrange the stuffed shells side by side in the greased baking dish.
Sprinkle the remaining shredded mozzarella cheese evenly over the top.
Cover the baking dish tightly with aluminum foil and bake for 20 minutes.
After 20 minutes, remove the foil and continue to bake for an additional 10 minutes.
Let the baking dish rest for a few minutes before serving. Garnish with sliced green onions.