01 - Preheat oven to 375°F (190°C). Grease a 9x13 inch baking dish lightly with olive oil or non-stick spray.
02 - Boil pasta in a large pot of salted water until just al dente, following package instructions. Drain and set aside.
03 - Heat olive oil in a large skillet over medium heat. Add diced onion and sauté for 2 minutes until translucent. Add minced garlic and cook for 1 minute, stirring frequently.
04 - Add sliced banana peppers to the skillet and cook for 2 minutes. Stir in shredded cooked chicken, salt, black pepper, and dried Italian herbs; cook for 2 more minutes until combined.
05 - Pour Alfredo sauce and whole milk into the skillet, stirring to combine. Simmer for 2 minutes until heated through.
06 - Remove skillet from heat. Mix in half of the shredded mozzarella and all of the Parmesan cheese until melted and creamy.
07 - Transfer cooked pasta to a large mixing bowl. Add the creamy chicken mixture, tossing until pasta is thoroughly coated.
08 - Spread the pasta and chicken mixture evenly into the prepared baking dish. Sprinkle the remaining mozzarella cheese over the top.
09 - Bake uncovered for 25 to 30 minutes until the top is golden and the filling is bubbling.
10 - Remove from the oven and allow to cool briefly. Garnish with chopped fresh parsley and serve hot.