01 - 
                Preheat the oven to 375°F and position a rack in the center. Lightly coat a 9x13 inch baking dish with olive oil spray to prevent sticking.
              
              
              
                02 - 
                Boil a large pot of well-salted water. Cook penne pasta until 2 minutes less than package instructions for al dente texture. Reserve 1 cup of pasta water, then drain the pasta.
              
              
              
                03 - 
                Melt butter in a large skillet over medium heat. Add minced garlic and cook for 30 seconds until fragrant without browning. Whisk in flour and cook 1 to 2 minutes until roux appears foamy and nutty.
              
              
              
                04 - 
                Gradually whisk in chicken broth followed by heavy cream, stirring constantly to avoid lumps. Simmer for 2 to 4 minutes until slightly thickened, resembling light gravy. Season with salt, black pepper, and dried oregano. Remove from heat and incorporate Parmesan and 1 cup mozzarella until smooth.
              
              
              
                05 - 
                Add cooked pasta and shredded chicken to the skillet. Toss thoroughly to coat. If mixture appears too thick, add reserved pasta water to maintain sauce consistency.
              
              
              
                06 - 
                Transfer the mixture evenly into the prepared baking dish. Sprinkle additional shredded mozzarella and a pinch of oregano over the surface for a light herb crust.
              
              
              
                07 - 
                Bake for 18 to 22 minutes until bubbling and the cheese is melted and lightly golden. Optionally, broil 1 to 2 minutes for a deeper golden color, monitoring closely to prevent burning.
              
              
              
                08 - 
                Allow the casserole to rest for 10 minutes so the sauce thickens and slices cleanly.
              
              
              
                09 - 
                If using raw chicken breast, dice 1 lb into bite-sized pieces and season lightly with salt and pepper. Incorporate raw chicken into sauced pasta, transfer to baking dish, cover tightly with foil, and bake for 30 to 35 minutes until chicken reaches 165°F internally. Remove foil, top with extra mozzarella, and bake an additional 10 to 12 minutes for browning.