Preheat the oven to 375°F.
Boil pasta in salted water according to package directions. Reserve 1 cup of pasta water and drain the rest. Set the noodles and reserved pasta water aside.
In a large oven-safe skillet over medium heat, melt the butter. Add the minced garlic and cook for 30 seconds.
Add the all-purpose flour to the skillet and whisk it together with the butter, cooking for 1 more minute.
Slowly drizzle in the milk and heavy cream, whisking constantly until the mixture thickens enough to coat the back of a spoon.
Add the parmesan cheese, ½ cup of shredded mozzarella cheese, onion powder, kosher salt, and black pepper. Continue to stir until the cheese is completely melted and the sauce is smooth.
Add the rotisserie chicken and cooked pasta. Stir to combine everything evenly with the sauce. If your sauce is too thick, add some reserved pasta water, stirring to combine.
Sprinkle the remaining shredded mozzarella cheese over the top of the dish.
Bake, uncovered, for approximately 20 minutes or until cooked through and lightly browned.
Garnish with finely chopped fresh parsley and serve.