Cook the whole wheat pasta in a large pot of salted boiling water until al dente, about 10 minutes. Drain and rinse under cold water.
In a medium bowl, combine Greek yogurt, mayonnaise, Dijon mustard, apple cider vinegar, and garlic powder. Whisk until smooth and creamy. Season with salt and pepper.
Chop the cherry tomatoes, cucumber, red bell pepper, and red onion into bite-sized pieces.
In a large bowl, combine the chopped vegetables, cooled pasta, and diced chicken. Pour the dressing over and toss gently to coat.
Cover and refrigerate for at least 30 minutes before serving. Garnish with fresh parsley if desired.