Preheat the oven to 375 degrees Fahrenheit.
Cook the rotini according to the package directions. Drain and set aside.
Add the cooked pasta, shredded chicken, finely chopped broccoli, Alfredo sauce, ranch seasoning, mozzarella cheese, and Colby Jack cheese to a 9x13-inch baking dish.
Stir everything together until well combined and evenly coated.
Bake for 15 minutes, or until the casserole is hot and the cheese is melted.
Let cool for a few minutes before serving.