Place the chicken breasts on a sheet of greaseproof paper and use a meat tenderiser to flatten it to a height of around 1cm. Grease the meat with the oil and season it with salt and pepper. Leave them to stand for half an hour to absorb all the flavourings. Meanwhile, ignite the gas barbecue or the chimney barbecue and bring it up to temperature; around 180 °C (356 °F). Once the gas/chimney barbecue is up to temperature, cook the chicken breasts for 7/8 minutes, turning them over once or twice.