Rub the chicken inside and out with a generous amount of salt and freshly ground black pepper. Leave for about 2 hours or overnight. Preheat oven to 400 F.
There's no need to peel the vegetables – just give them a good wash and roughly chop them. Break the garlic bulb into cloves, leaving them unpeeled. Put all the vegetables and garlic into the roasting tray and drizzle with olive oil. Drizzle the chicken with olive oil too. Carefully prick the lemon all over, using the tip of a sharp knife or a fork. Put the lemon inside the chicken's cavity, with the bunch of thyme. Place the chicken on top of the vegetables in the roasting tray and put it into the preheated oven. Roast the chicken for about 70-80 minutes. Remove the chic hen from the oven, cover it with a foil and let to rest for 7-10 minutes before serving.