Preheat oven to 425°F (220°C). Use a chef’s knife or kitchen shears to cut down both sides of the backbone. Remove the backbone and discard. Cut the top of breastbone so that the chicken lays flat (optional, remove keel bone at bottom of breasts and discard for a flatter chicken).
Carefully rinse chicken, pat dry with a paper towel, and season with salt and pepper.
Brush peri-peri sauce on both sides of the chicken, let marinate for an hour or overnight, optional.
Heat a large cast-iron skillet with oil over medium-high heat. Place chicken skin side down and sear until browned for approximately 5 minutes. Add lemons around chicken cut side down, sear for 1-2 minutes, remove lemons from pan, set aside.
Place a sheet of aluminum foil loosely over the chicken, add another heavy cast iron pan on top of the chicken to weigh it down, transfer to the oven and roast for 25-30 minutes, or until an instant-read thermometer is inserted into the thickest part of the meat registers 160˚F (71˚C).
Serve on a platter with the lemon, garnish with parsley.