In a mixing bowl combine the orange juice, zest, vinegar, sea salt, brown sugar and Simon Gault Home Cuisine Mexican seasoning. Place the chicken into the bowl and coat well with the marinade. Heat the BBQ to a medium heat. Lightly brush the grill with oil. Remove the chicken from the marinade, reserving the left over liquid. Place the chicken onto the grill skin side down, cook for 4 to 5 minutes to give the skin char marks, turn the chicken over so that its skin side up, baste with the reserved marinade. Cover the grill and cook for 35 minutes or until the chicken is cooked right through or has an internal temperature of 74 °C. Take the chicken of the grill and allow to rest for 10 minutes before serving. To serve cut the cooked chicken into quarters and sprinkle with chopped oregano.