Bring a large pot of salted water to a boil and cook pasta according to package directions until al dente. Drain and rinse under cold water, then let cool completely. In a large bowl, combine cooled pasta and diced chicken. In a small bowl, mix Caesar dressing with lemon juice, garlic powder, and black pepper. Pour dressing over pasta and chicken and toss until evenly coated. Gently fold in chopped romaine and grated Parmesan cheese. Just before serving, add crushed croutons and toss lightly. Serve chilled or slightly cool.