Preheat oven to 425°F.
Dice rotisserie chicken pieces. Mince garlic (if not using garlic powder).
In a large 13 x 9-inch baking dish, stir together uncooked pasta, Alfredo sauce, chicken broth, chicken, garlic, red peppers, and sun-dried tomatoes. Cover tightly with aluminum foil and bake for 35 minutes.
Uncover; stir. At this point you should check the pasta to make sure that it is al dente (firm but just about finished cooking). If it’s still too hard, cover the dish and return to the oven until pasta is al dente. Then move on to the next step.
Once pasta is al dente, stir in the fresh spinach. The spinach will wilt almost instantly as you stir it into the hot pasta.
Sprinkle mozzarella over the top. Bake uncovered for 10 more minutes (or until cheese is melted and pasta is tender).