Cook the rotini pasta according to package directions until al dente. Drain immediately after cooking and rinse thoroughly with cold water to stop the cooking process and remove excess starch. Set aside to drain completely.

While the pasta cooks, prepare the ranch dressing. In a medium bowl, whisk together the mayonnaise, buttermilk, dried dill, onion powder, minced garlic, chives, salt, and pepper until completely smooth and well combined. Taste and adjust seasoning if necessary.

Cook the bacon in a skillet until crispy. Remove the bacon, let it cool slightly on paper towels, and then crumble it into small pieces.

In a large mixing bowl, combine the cooled, drained pasta, crumbled bacon, and halved cherry tomatoes.

Pour about three-quarters of the prepared ranch dressing over the pasta mixture. Gently toss everything together until the pasta and mix-ins are evenly coated.

Gently fold in the shredded iceberg lettuce last to maintain its crunch. Add more dressing if you prefer a creamier salad, saving some for serving if desired. Chill for at least 30 minutes before serving to allow the flavors to meld.