Mix together the ingredients for the marinade and then rub them all over the chicken and set aside to sit for as long as you can (up to 24 hours). The longer you leave it, the better.
Cut the onions into 1cm (½") thick slices and peel off the outer skin.
Lay the onion slices onto a roasting tin, then place the marinated chicken on top.
Transfer the roasting tin to the oven and cook at 200°C or 400°F for 30-35 minutes, then rest for 5-10 minutes covered with foil.
You are looking for an internal temperature of at least 73°C or 165°F after resting. I prefer to cook chicken legs to a higher temperature and aim for around 80°C. or 175°F