Frozen chicken that you buy in stores is usually just chicken that was slaughtered and then gets the meat such as the chicken legs, chicken breast etc separated.
I have heard that the chicken that you buy in the store such as the frozen chicken does contain a preservative so I guess if it does have a preservative in the chicken that the frozen chicken could be considered a processed food.
But it can depend on the company who processes the chicken but either way I would say any food you buy in the store is processed because it does come from a processing plant.
Other foods such as the chicken patties, nuggets and tenders are all also processed foods.