1. Put the peppers, onion, garlic and chillies (if using) in a roasting pan. Season with the spices and drizzle the lemon juice and olive oil over. Season with salt and pepper.
2. Roast for 20 minutes or until soft. Allow to cool then blend into a peri-peri paste.
3. To spatchcock the chicken, place it breast down on a kitchen surface. Use scissors to cut along either side of the backbone and discard the bone. Turn the chicken breast up and press down with the heel of your hand to open out and flatten the chicken.