Bring a large pot of salted water to a boil. Add the rotini pasta and cook according to package directions until al dente.
Drain the pasta and rinse under cold water to stop the cooking process. Set aside and allow it to cool completely.
In a medium bowl, whisk together the mayonnaise, ranch seasoning mix, milk, and black pepper until smooth. In a large mixing bowl, combine the cooled pasta, cherry tomatoes, green onions, and crumbled bacon.
Pour the dressing over the pasta mixture and toss until everything is evenly coated.
Just before serving, gently fold in the shredded romaine lettuce.
Serve immediately or refrigerate until ready to serve.