Preheat oven to 160°C fan forced. Heat 2 tbs oil in a stovetop, ovenproof dish over medium heat. Add the leek, garlic and mushrooms and cook, stirring occasionally for 5 minutes or until onions are soft. Add the rice and cook, stirring for 1 minute. Add the stock and bring to the boil.
Remove the dish from the heat, cover with lid or foil and transfer to the oven. Bake for 18-20 minutes or until the stock is almost absorbed.
Meanwhile, heat remaining oil in a non-stick frying pan over medium heat. Add chicken and cook for 5 minutes each side until just cooked through. Remove to a board, stand for 5 minutes then thinly slice.
Stir the chicken, basil and parmesan into the risotto. Season with pepper. Scatter over the basil leaves and serve.