In a small bowl, whisk together the ranch dressing mix, mayonnaise, sour cream, and milk until smooth, then refrigerate while preparing the salad.
In a large mixing bowl, combine the cooked rotini pasta, cubed grilled chicken, cubed cheddar cheese, halved cherry tomatoes, chopped bacon, sliced green onions, and chopped parsley.
Pour the prepared dressing over the pasta mixture and stir until everything is evenly coated.
Cover and refrigerate for at least 30 minutes to allow the flavors to meld before serving.
Stir the salad before serving and garnish with additional parsley or green onions if desired.