If using a frozen chicken, defrost it in the fridge a day in advance.
To prepare the marinade: Combine all the ingredients for the marinade in a food processor or blender and blend until smooth.
Place the whole chicken in a large resealable bag or bowl.
Now, pour the marinade over the chicken, making sure it's fully coated.
Cover or seal, then refrigerate for at least 8 hours, ideally overnight.
Flip the chicken once or twice during marinating if possible.
About 30 minutes before cooking, remove the chicken from the fridge to bring it to room temperature.
Preheat the oven to 425°F. Place a rack in a roasting pan and set the chicken breast-side up. Truss the legs if desired.
Roast the chicken for 1 hour to 1 hour 15 minutes. Baste once or twice with pan juices.
As the chicken roasts, prepare the green sauce: In a clean blender, combine all the sauce ingredients and blend until creamy and smooth Chill until time to serve.
Once the chicken reaches an internal temperature of 165°F at the thickest part of the thigh, remove it from the oven and let it rest for 10–15 minutes.
Carve into pieces and serve hot with the aji on the side and topped with any remaining parsley. Enjoy!