Set your oven to 350°F (175°C) and let it heat up. This ensures the casserole bakes evenly for a perfect, golden finish.
Add the chicken to a pot and cover with water. Bring to a boil, then lower the heat and simmer for about 15 minutes, or until the chicken is fully cooked through and the juices run clear. This ensures the chicken is tender and safe to eat.
Meanwhile, bring a pot of salted water to a boil. Add the penne and cook for around 11 minutes, stirring occasionally, until it's tender but still slightly firm. Drain the pasta and set it aside for the casserole.
Once the chicken is cooked, drain it and slice it into bite-sized chunks for easy mixing into the casserole.
Combine the chicken, cooked pasta, Alfredo sauce, half of the mozzarella cheese, milk, onion powder, and garlic powder in a large bowl. Stir thoroughly to coat everything evenly.
Transfer the mixture into a 1 1/2-quart casserole dish. Top with the remaining mozzarella and a layer of Cheddar cheese for a cheesy, golden finish.
Place the casserole in the preheated oven and bake for about 25 minutes, or until the cheese is melted and the dish is bubbling with golden perfection.