Cook tortellini according to package directions. Meanwhile, in a small bowl, combine the mayonnaise, milk, 1/4 cup Parmesan cheese, lemon juice and garlic. , Drain tortellini and rinse in cold water; transfer to a large bowl. Add romaine and remaining Parmesan. Just before serving, drizzle with dressing; toss to coat. Top with croutons and tomatoes if desired.