Step 1: Bring a large pot of salted water to a rolling boil. Add the rotini pasta and cook according to package instructions until al dente, usually about 8 to 10 minutes. Drain the pasta well and set it aside.

Step 2: While the pasta cooks, season the chicken pieces with Italian seasoning, salt, and black pepper. Heat the olive oil in a large, deep skillet over medium-high heat. Add the chicken in a single layer and cook for 6 to 8 minutes, turning occasionally, until the chicken is golden brown and cooked through. Remove from the skillet and keep warm.

Step 3: Lower the heat to medium. In the same skillet, melt the unsalted butter. Add the minced garlic and sauté for about 1 minute until fragrant but not browned.

Step 4: Sprinkle the flour into the butter and garlic mixture, whisking constantly for about 1 minute. This creates a roux that will thicken the sauce.

Step 5: Slowly pour in the milk while whisking continuously to keep the sauce smooth. Let the sauce simmer gently for 3 to 4 minutes until it thickens slightly.

Step 6: Stir in the grated Parmesan and 1 cup of the shredded mozzarella cheese. Mix until the cheeses have fully melted and the sauce is creamy and velvety. Season with garlic powder, salt, and freshly ground black pepper to taste.