Spray a large baking dish with cooking spray.
Season your chicken pieces on both sided with salt, pepper, and garlic powder. Place them in the pan and bake for 20 minutes at 400°.
While the chicken is baking, place the cream cheese in a large non-metallic bowl and microwave for 30 seconds to soften.
Once the cream cheese is softened, add into the bowl the spinach (thawed - you can do this in the microwave), mayonnaise, dill, celery seed, garlic, and parmesan. Mix thoroughly.
After the 20 minutes of baking, take the chicken out of the oven and cover it with the spinach and artichoke mixture.
Adjust the temperature of the oven to 350° and then bake for 15 minutes.
Next, sprinkle the shredded Italian cheese over the top. Bake 5 more minutes to melt the cheese, then enjoy!