Preheat the oven to 350 degrees F (180 degrees C). Grease a 2-quart casserole dish.
Bring a large pot of water to a boil; add pasta and cook until tender with a bite, 8 to 11 minutes. Drain and set aside.
Meanwhile, heat a nonstick skillet over medium-high heat, and cook chicken for 4 minutes; flip and cook until no longer pink at the center and juices run clear, 3 to 4 minutes more. Let chicken rest for 5 minutes, then chop into bite-sized pieces.
Mix pasta, chicken, Caesar dressing, chicken broth, green onion, and mozzarella together in a large bowl. Pour into the prepared casserole dish. Top dish with croutons and sprinkle with Parmesan cheese.
Bake in the preheated oven until croutons are golden brown, about 20 minutes. Serve warm.