Step 1: Cook the pasta according to package directions until al dente. Drain well and rinse with cold water to stop the cooking process and cool the pasta. Set aside.
Step 2: While the pasta cooks, prepare the dressing. In a large bowl, whisk together the mayonnaise, sour cream (or Greek yogurt), Dijon mustard, apple cider vinegar, garlic powder, onion powder, salt, and pepper until smooth and well combined. Taste and adjust seasonings as needed.
Step 3: Add the cooled, drained pasta to the bowl with the dressing. Gently toss to coat all the pasta evenly.
Step 4: Add the diced cooked chicken or turkey, crumbled bacon, halved cherry tomatoes, finely diced red onion, and finely diced celery to the pasta mixture.
Step 5: Gently fold all the ingredients together until everything is well distributed and coated in the creamy dressing.
Step 6: Cover the bowl and refrigerate for at least 1-2 hours to allow the flavors to meld and the salad to chill. For best results, chill for at least 4 hours, or even overnight.
Step 7: Just before serving, stir in the fresh chopped parsley and, if using, the shredded lettuce. Serve chilled.