Bring a large pot of salted water to a rolling boil over high heat. Add the rotini pasta and cook for 8-10 minutes, or until al dente. Drain and rinse under cold water to halt cooking.

Dice the cucumber, halve the cherry tomatoes, and finely chop the red onion. Place them in a large mixing bowl.

In a medium bowl, combine mayonnaise, sour cream, lemon juice, garlic powder, dried dill, salt, and pepper. Whisk until smooth.

Add cooled pasta to the vegetable bowl and pour the dressing over everything. Toss gently to combine.

Cover and chill in the refrigerator for at least 30 minutes before serving to let the flavors meld.

Stir gently before serving and garnish with fresh dill if desired. Serve as a side at barbecues or picnics.