In a bowl, combine all the ingredients. Set aside.
In a bowl, combine the spices and the salt. Set aside.
On a work surface, with a sharp knife or kitchen shears, cut along one side of the backbone of the chicken. Open the chicken and spread it out flat. Gently lift the skin from the breast and legs, without tearing it, to allow the marinade to seep into the meat.
Place the chicken in a large glass dish or large sealable plastic bag. Rub the chicken with the spice mixture. Add half the chimichurri sauce and thoroughly coat the chicken. Cover the dish or seal the bag and refrigerate for 12 hours. Refrigerate the remaining sauce until ready to serve.
Preheat one side of the grill, setting the burner to high. Oil the grate on the unheated side.
Lay the chicken flat on the unheated side of the grill, skin side down. Close the lid. Discard the marinade.
Cook for 45 minutes. Flip the chicken and continue cooking for about 35 minutes or until a thermometer inserted into the thigh, without touching the bone, reads 180°F (82°C). Brush the chicken with chimichurri sauce a few times during cooking. Finish cooking the chicken on the heated side to create char marks.
Serve the chicken with the reserved chimichurri sauce.