Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Add the pasta and cook until al dente. Drain well. Wash and chop the lettuce.
In a small bowl, whisk the milk, mayonnaise, and ranch mix. In a large bowl, toss the cooked pasta, lettuce, tomatoes, bacon, and green onions together. Add the dressing and toss to combine. Season to taste with salt and freshly ground black pepper