Remove chicken from refrigerator about 30 minutes prior.Preheat oven to 200℃.Drip 2 tablespoons of olive oil in a roasting pan, add the onions, garlic and lemon slices and, with your hand, mix it all together until everything is coated with the oil.Move the vegetables to the side and add the chicken. Rub the remaining 1 tablespoon olive oil into the chicken. Season well with salt and black pepper and arrange the vegetables around the chicken. Drape the sprigs of thyme over the chicken and vegetables.Roast the chicken for 1 hour. Don't be alarmed if the onion and lemons start crisping to black at the edges - it will all be worth it in the end! Once chicken is cooked through, remove from the oven. Cover with foil and let it all rest for 20 minutes. Don't skip this step!