Bring a large pot of salted water to a boil. Add the fettuccine pasta and cook according to package instructions until al dente. Drain the pasta and set aside.
If using leftover cooked chicken, shred it finely with your hands or forks. Toss the shredded chicken with olive oil, garlic powder, Italian seasoning, salt, and pepper to infuse flavor.
In a large mixing bowl, combine the Alfredo sauce, shredded mozzarella, and grated Parmesan cheese. Stir until the cheeses are evenly distributed throughout the sauce.
Add the cooked pasta and seasoned chicken into the bowl with the Alfredo sauce mixture. Gently fold everything together until the pasta and chicken are completely coated with the creamy sauce.
Lightly grease your baking dish with a bit of olive oil or nonstick spray. Pour the creamy pasta and chicken mixture into the dish and spread it evenly.
Preheat your oven to 350°F (175°C). Bake the casserole uncovered for 25-30 minutes, or until the top is bubbly and golden brown.
Remove the bake from the oven and let it rest for 5 minutes. Sprinkle freshly chopped parsley over the top for a burst of color and fresh flavor. Serve warm and enjoy!