Pour rice into a fine-mesh strainer, rinse thoroughly with cold water, transfer to a saucepan, cover with equal volume of water, cover, and boil for 5 minutes. Thinly slice the radicchio then add it to the rice, stir, cover, simmer for a few minutes, turn off, and let your rice rest until it is time to complete the preparation. Now put your rice back on the stove, add a little water, until the rice is covered, and bring it to cook. When cooked, stir-fry, assess the density of the risotto, add a little water if necessary, add salt, season with pepper and lemon zest, and stir until the desired density is reached; when the heat is off if desired, add 1 tablespoon of extra virgin olive oil. Serve by sprinkling the surface with chopped walnuts.