Place the stock in a small saucepan and bring to simmering point.
Meanwhile, heat the olive oil in a large saucepan. Add the yellow pepper and fry, stirring often, until the pepper has softened but not browned. Add the rice and continue cooking and stirring for 1-2 minutes, until the rice is translucent and shiny.
Pour the wine into the pan of rice and simmer until it has almost evaporated. Add a ladle of the hot stock to the rice and cook, stirring constantly, over a low heat until the liquid has been absorbed. Continue adding the stock to the rice a little at a time and stirring until the liquid has been absorbed, for about 17 minutes.
When the rice is almost done, add the chicken and the spinach leaves and stir to mix evenly. Allow to heat through for 2-3 minutes, then adjust the seasoning to taste with salt and pepper and serve hot.