Cook the pasta in salted water until just al dente, then drain and rinse with cold water. Let it sit for a few minutes to fully cool before mixing.
Open the canned chicken, drain it completely, and break it apart with a fork. Remove any overly soft bits if needed.
In a large bowl, mix mayonnaise, Greek yogurt, Dijon mustard, lemon juice, garlic powder, salt, and pepper until smooth and slightly glossy. Adjust salt or lemon to taste.
Add the cooled pasta, chicken, celery, red onion, and corn into the bowl. Toss everything together until evenly coated with the dressing.
Cover the bowl and refrigerate for at least 30 minutes. Before serving, give it a quick stir and sprinkle fresh parsley on top if using.