Boil pasta in salted water according to package instructions. Drain, rinse under cold water, and set aside.
If using raw chicken, season with salt/pepper, cook until done (165°F), then dice.
Chop tomatoes, cucumber, bell pepper, red onion, and olives.
In a bowl, whisk mayo, sour cream, vinegar, sugar, garlic powder, salt, pepper, and parsley.
In a large bowl, mix pasta, chicken, vegetables, and cheese (if using).
Pour dressing over and toss gently to coat.
Cover and refrigerate for at least 1 hour (best if chilled 4+ hours).
Stir before serving. Garnish with extra parsley or paprika if desired.
