Begin by bringing a large pot of salted water to a rolling boil. Add the whole wheat pasta and cook according to package instructions until al dente (about 8-10 minutes). Drain the pasta and let it cool completely.

In a medium-sized mixing bowl, combine plain Greek yogurt, Dijon mustard, and olive oil. Whisk until smooth and creamy. Taste and season with salt and pepper.

In a large mixing bowl, add cooled pasta, chopped chicken breast, finely chopped celery, and halved cherry tomatoes. Gently fold together using a spatula.

Pour the prepared dressing over the salad mixture. Toss everything together gently until all ingredients are coated with the dressing.

Cover the mixing bowl with plastic wrap and chill the salad in the refrigerator for at least 30 minutes before serving. Serve chilled as a light lunch or at a picnic.