Bring a large pot of salted water to a boil and add the rotini pasta. Cook according to package directions, usually about 8–10 minutes, until al dente. Drain and rinse under cold water.

In a large skillet, heat over medium heat and cook the bacon strips until crispy, about 5–7 minutes. Transfer to paper towels to drain excess fat.

In a mixing bowl, whisk together mayonnaise and a splash of milk or buttermilk until smooth. Adjust thickness as needed.

In a large mixing bowl, combine the cooled rotini pasta, crumbled bacon, and diced tomatoes. Pour the creamy dressing over and gently stir until well coated.

Right before serving, fold in the chopped romaine lettuce to maintain its crispness.

Cover and chill the pasta salad in the refrigerator for at least 15 minutes before serving.