Place the leek and 3 tablespoons of the chicken stock in a large saucepan. Bring to a boil, and cook for about 5 minutes, until leek is tender. Add the rice, and the remaining chicken stock, and bring to a boil. Reduce heat to low, cover, and simmer for about 20 minutes, or until all of the liquid has been absorbed.
Meanwhile, preheat the oven to 200 degrees C (400 degrees F). Lightly grease a 24cm (9 inch) springform pan.
When the rice is tender, remove the pan from the heat, and stir in the lemon zest, chives, parsley and mozzarella cheese. Season with salt and pepper. Spoon into the springform pan, and spread evenly. Cover the top of the pan with aluminum foil.
Bake for 30 to 35 minutes in the preheated oven, or until firm and lightly browned. Run a thin spatula or knife around the outer edge of the pan, and invert the cake onto a serving plate. Serve hot or cold, sliced into wedges. Garnish with parsley and lemon wedges.