Cook the Pasta: Bring a large pot of salted water to a rolling boil, then add the rotini or penne pasta. Cook according to package directions until al dente, about 8-10 minutes. Drain and rinse under cold water. Set aside to cool completely.

Prepare the Bacon: Cook bacon strips in a skillet over medium heat until crispy and golden, about 5-7 minutes. Transfer to a plate lined with paper towels to drain, then cool and crumble.

Whisk the Dressing: In a mixing bowl, combine mayonnaise, sour cream, ranch seasoning, and buttermilk. Add garlic and onion powder, salt, and pepper. Whisk until smooth and creamy.

Combine Salad Ingredients: In a large mixing bowl, add cooled pasta, crumbled bacon, halved cherry tomatoes, diced red onion, and shredded cheddar cheese. Gently combine with a spatula.

Dress the Salad: Pour the creamy dressing over the pasta mixture and gently fold until everything is coated.

Add Freshness at the End: Fold in chopped romaine lettuce just before serving.

Chill and Serve: Cover with plastic wrap and refrigerate for at least 30 minutes before serving.