Preheat oven to 375F/190C. Spray a baking dish with non-stick spray, choosing a dish just large enough to hold the chicken.
Trim chicken breasts well, cutting larger ones in half if desired.
Put each piece of trimmed chicken inside a small Ziploc bag and pound with a meat mallet (or something heavy), just until the chicken is an even thickness, about 1/2 inch thick. Don't pound too hard or too long or the chicken breasts will start to shred apart. Then cut small shallow crosswise slits going down each chicken breast, being careful not to cut through.
Mix the mayo, poultry seasoning, garlic powder, and black pepper, then stir in the coarsely grated Parmesan.
Put chicken breasts into the baking dish and use a rubber scraper to spread the mayo-Parmesan coating over the top of each chicken breast, covering the entire surface.
Bake chicken for 35-40 minutes, or until the chicken is firm and the top is nicely browned. There will be some liquid and congealed cheese in the bottom of the baking dish, but just ignore it and move the chicken breasts to a serving platter. Several other places where I spotted similar recipes also mentioned this, so I'm not sure if there is a way to avoid it.
Serve hot, and wait for compliments!
