Season the chicken breasts with olive oil, salt, pepper, and garlic powder. Cook in a skillet over medium-high heat, on the grill, or in the air fryer at 375°F for 12 to 15 minutes, until the internal temperature reaches 165°F. Rest 5 minutes, then slice into strips.
Bring a large pot of salted water to a boil. Cook the rotini one minute short of the package directions for al dente. Reserve 1/2 cup pasta water, then drain.
In a saucepan over medium heat, melt the butter. Add the minced garlic and cook 30 seconds, just until fragrant.
Pour in the heavy cream and bring to a gentle simmer. Do not let it boil.
Whisk in the cubed cream cheese until completely melted and smooth.
Reduce heat to low. Add the Parmesan a handful at a time, whisking constantly until smooth. Season with salt, pepper, and nutmeg.
In a large bowl, fold the drained pasta and sliced chicken into the sauce until evenly coated. Loosen with reserved pasta water if needed.
Transfer to a baking dish that fits your air fryer basket, or a 9x13-inch pan for the oven. Top evenly with shredded mozzarella.
Air fryer: preheat to 360°F and bake 8 to 12 minutes, until the cheese is melted, bubbling, and browned in spots. Oven: bake at 375°F for 18 to 20 minutes, then broil 2 minutes for a golden top.
Rest 5 minutes. Garnish with Parmesan and chopped parsley, and serve warm.