1.Heat half oil in a heavy-based saucepan on medium. Add chicken and cook 2-3 minutes, until cooked through. Transfer to plate. Cover and keep warm.
2.Heat remaining oil in same saucepan on medium. Sauté mushroom, leek and half the parsley for 1-2 minutes, until starting to soften. Season to taste. Stir rice through. Cook for 1 minute.
3.Stir in 1 cup of hot stock and cook, stirring, until stock is absorbed. Continue adding stock 1 cup at a time until each addition is absorbed, stirring and simmering for about 20-25 minutes, until risotto is tender and creamy.
4.Stir chicken and remaining parsley through. Season to taste. Cook a further 2-3 minutes. Top with parmesan cheese and onion.