Preheat the oven to 425°.
First, remove any giblets or packaging from the chicken cavity and give a good thorough rinse under cold water. Be sure to rinse both the inside and outside of the bird. When the water runs clear, use a paper towel or a clean dish towel to dry the chicken off.
Slice the carrots and celery in thicker pieces and scatter around your cast iron skillet.
Slice a whole onion into thick chunks and scatter within the skillet as well.
Drizzle the vegetables with a tbsp of olive oil and season with salt and pepper.
Take the fryer and generously season the cavity with salt and pepper.
Next, stuff the cavity with a half of a lemon and a half of an onion. You can slice the onion into a couple of pieces if need be.
Take the last 2 tbsp. of olive oil and coat the outside of the bird. Be sure to get all over and don't forget the wings and legs.
Generously season the outside of the bird with salt and pepper. Don't be shy.
Place the stuffed bird on top of the vegetables and put on the center rack in the oven for 90 minutes.
Every 30 minutes baste the chicken with the juices at the bottom of the pan.
When the internal temperature of the bird reaches between 155° and 165° remove it and let it sit for at least 30 minutes.