Bring a large pot of salted water to a boil. Cook the rotini pasta according to package directions until al dente (typically 8-10 minutes). Drain pasta and rinse under cold water to stop the cooking process immediately.
In a small bowl, whisk together ranch dressing, mayonnaise, lemon juice, garlic powder, and dried dill until smooth and well combined.
In a large mixing bowl, add the cooled pasta, diced chicken, crumbled bacon, cherry tomatoes, cucumber, and red onion. Pour the dressing over the ingredients and gently toss until everything is evenly coated. Season with salt and pepper to taste.
Cover the bowl and refrigerate for at least 30 minutes, ideally 2 hours. This resting period allows the flavors to meld together.
Just before serving, gently fold in the diced avocado. Garnish with fresh chopped parsley if desired.