Prepare the pasta: Bring a large pot of water that has been salted to a boil. After adding the rigatoni, cook for 8 to 10 minutes, or until al dente. After draining, set aside.
Sauté the garlic: In a large skillet, heat olive oil and butter over medium heat. Add minced garlic and sauté for 30-60 seconds until fragrant, stirring to prevent burning.
Make the creamy sauce: Sprinkle flour over the garlic and stir for 1 minute to form a roux. To prevent lumps, whisk in the milk and chicken broth gradually while stirring continuously. Cook until the sauce slightly thickens, 3 to 4 minutes.
Add cheese and seasonings: Stir in 3/4 cup Parmesan cheese, 1/2 cup mozzarella, Italian seasoning, garlic powder, salt, and pepper. Mix until the cheese melts into a smooth, creamy sauce.
Combine ingredients: In a large mixing bowl, toss the cooked pasta, shredded chicken, and creamy garlic parmesan sauce until well-coated.
Assemble the bake: Preheat your oven to 375°F (190°C). Pour the pasta mixture into a 9 x 13-inch baking dish that has been oiled. Sprinkle the remaining 1/2 cup of mozzarella and 1/4 cup of parmesan on top for a cheesy crust.
Bake the casserole: Bake for 20-25 minutes until the cheese is golden and bubbly. For a crispier top, broil for 1-2 minutes at the end, watching closely to avoid burning.
Garnish and serve: Remove from the oven, sprinkle with fresh parsley, and serve warm with a side salad or garlic bread.
