Pat the chicken dry with paper towels and season generously with salt, in and out. This is the way to dry brine your chicken. Let it sit the refrigerator to a couple of hours or overnight. But it you don't have enough time, 1 hour will do. Using your mandoline slicer, slice the onions and potatoes, or if you are using your knife just slice it thinly. Set aside.
Mix olive oil, the juice of the lemon, and garlic.
Add half of your olive oil/lemon mixture and 1/2 tbsp of greek seasoning to the sliced onion and potatoes. Mix to combine. Arrange the mixture in the pan. Set aside. Preheat oven to 475 degress F.
Meanwhile, brush the rest of your olive oil mixture to your chicken and then rub the remaining greek seasoning to the chicken.
Place the chicken on top of potato and onion.
Place it in the oven (uncovered) and bake for 15 minutes then adjust the oven temperature to 350 degrees F and roast it for another 50 minutes to 1 hour, depending on the size of your chicken. Using a meat thermometer, insert it to the thickest part of breast, if the reading is 165 degrees then your chicken and potatoes are done.