Preheat the oven to 300°. Halve the lemon. Cut 3 very thin slices from 1 half; halve the slices. Squeeze 1 tablespoon of juice from the other lemon half and reserve. Using your fingers, carefully loosen the skin over the chicken breasts and thighs; do not tear the skin. Stuff the lemon slices, 8 of the sage leaves and the parsley under the skin. Season the cavity with salt and pepper, then stuff it with the remaining lemon, 3 sage leaves, 1 thyme sprig and 2 garlic cloves. Rub 1 tablespoon of the oil over the chicken; season with salt and pepper. Tie the legs together with kitchen string.