Preheat the oven to 375°F (190°C).
Cook pasta according to package instructions until al dente, drain.
In a mixing bowl, combine cream cheese, sour cream, half of the cheddar cheese, and ranch dressing mix. Stir in the cooked chicken.
Mix the cooked pasta into the chicken mixture, then transfer to a greased baking dish.
Top with the remaining cheddar cheese.
Bake for 25 minutes or until bubbly and golden.
Garnish with green onions before serving.
