Preheat the oven to 220C.
Warm the lemon in the microwave for 40 seconds.
Prick the lemon with a knife.
Mix the herbs, salt, pepper, and olive oil together and divide it into two portions.
Gently pull the chicken skin towards yourself to separate it from the breast.
Place half of the herb mixture and a tablespoon of butter under the skin of each breast.
Tie the legs together with butcher's string.
Place the chicken, onions, and garlic in a tray.
Roast the chicken in the oven for one hour.
Check if the chicken is cooked by pulling the meat off the bone easily and checking that the juices run brown.
Let the chicken rest before serving.
