On a work surface, with a chef’s knife or kitchen scissors, cut out the backbone of the chicken. Turn the chicken over and cut it in half. Transfer to a large glass dish. Sprinkle the salt and garlic powder over the chicken skin. Rub the chicken halves all over with the cut side of the lemon. Coat well with ½ cup (125 ml) of the ranch dressing. Cover and refrigerate for 12 hours.
Preheat half of the grill, setting the burners to high. Oil the side of the grill that is off.
Drain the meat from the marinade. Place the chicken pieces on the side of the grill that is off, skin side down. Close the lid and cook for 45 minutes, maintaining a temperature of 400°F (200°C). Turn the chicken over and continue cooking for 35 minutes or until a thermometer inserted in the thigh without touching the bone reads 180°F (82°C). Transfer the chicken to the hot side of the grill to obtain nice grill marks.
Meanwhile, in a bowl, combine all of the ingredients. Season with salt and pepper.
Cut the chicken into pieces. Serve with the salad and remaining ranch dressing.