Preheat the oven to 425°F / 220°C / Gas Mark 7 (no fan, if you have a convection oven reduce the temperature by about 20° or follow the manufacturer's instructions).
Pound the chicken breast in its thickest part slightly (it will bake more evenly). Don't pound it too much - it should still resemble chicken breasts and not chicken cutlets. Season with salt and pepper on both sides (be careful with salt, Parmesan cheese is already salty).
In a small bowl stir the mayo, grated cheese, Italian seasoning, and garlic powder together.
Spread the mayo-cheese paste on the chicken, making sure it's covered on all sides (spread more paste on top of the meat).
Bake for about 17-19 minutes depending on the size of the breasts. To be sure if they're done, measure the internal temperature of the meat with a meat thermometer. Insert it into the thickest part of the meat - the temperature should be 158°F/70°C (the safe temperature for poultry is 165°F/74°C, the meat should come to this temperature after the resting time).
Let rest for 5-10 minutes then serve.
Enjoy!