Cook the rotini pasta according to package instructions. Drain and rinse under cold water to cool. Set aside.
In a large bowl, combine the diced cucumber, halved cherry tomatoes, and chopped red onion.
In a separate bowl, whisk together the mayonnaise, sour cream, apple cider vinegar, garlic powder, dried dill, salt, and pepper until smooth.
Add the cooled pasta to the vegetable mixture and pour the dressing over the top. Toss gently until everything is well coated.
Cover the salad and refrigerate for at least 30 minutes to allow the flavors to meld.
Before serving, give the salad a gentle stir and garnish with fresh dill if desired.