Take your whole chicken, cut it in half (you can also remove the spine if desired) and place in roaster pan.
Wash and quarter potatoes, put in large bowl.
Cut large lemon in half. Squeeze juice onto chicken -- 1/2 lemon for each 1/2 chicken -- then rub chicken with the squeezed out cut lemon halves.
Pour olive oil onto chicken. I used about 1/3 cup because this chicken was so huge, but 1/4 cup would do for a more moderately sized bird.
Season to taste with Kosher salt, pepper, garlic (I used a couple of tablespoons minced garlic) and a generous amount of oregano.
Season potatoes with about 1/2 cup olive oil, the juice of your second lemon, salt, pepper, oregano, and garlic. Again to taste, but be generous with the oregano.
Arrange potatoes around chicken in baking pan, and then pour in the rest of the "juice" from your potatoes bowl.
Bake at 350 until done. Mine went an hour and forty minutes, but again: BIG FAT Greek Chicken. If yours is smaller, start checking it at about an hour fifteen and cook until it hits 165 degrees internal temp or juices run clear.
Notes
My Big Fat Greek Chicken is naturally gluten free & dairy free.