Peel and finely dice the onion and sauté in 2 tablespoons of oil until transparent. Add rice, sauté briefly and deglaze with vegetable stock and tomato pieces. Season with salt and pepper. Let simmer for about 20 minutes.
In the meantime pluck sage leaves from the stalks. Carefully remove the skin of the legs from the meat with your finger. Push several sage leaves under the skin. Rub the legs with salt and pepper and fry in remaining oil in a pan on all sides until golden brown.
Fry over medium heat for about 12 minutes. Finely chop remaining sage leaves and sprinkle over the risotto. Arrange chicken legs on top. Garnish as desired with a sprig of sage.