Set your oven to 350°F (175°C) and let it warm up.
Prepare the penne pasta by boiling it until just tender, then drain and keep it aside.
Warm the olive oil in a large skillet on medium heat; toss in the cooked chicken along with garlic powder, salt, and pepper, stirring until the seasoning covers every piece.
In a spacious bowl, stir together the pasta, the seasoned chicken, Alfredo sauce, mozzarella, Parmesan, and peas until evenly blended.
Pour this mixture into a greased 9x13-inch casserole dish, smoothing the top out.
Add a sprinkle of mozzarella and Parmesan over the surface to create a cheesy crust.
Place the dish in the oven and bake for about 25 to 30 minutes, or until the cheese is bubbling and has turned a nice golden color.
Take the casserole out and allow it to rest for a few minutes before serving; finish by adding chopped fresh parsley if you like.