Put a large saucepan or casserole (one with a lid) over a medium high heat and add a 2 tbsp of the olive oil. Add the chicken and cook for 3 to 5 minutes, stirring occasionally, until browned all over, then transfer to a plate or bowl, and set aside.
Add the other tbsp of olive oil to the pan followed by the onion, pepper, chilli (if using) and garlic, with a pinch of salt. Turn the heat down to low medium and cook for 10 minutes, stirring frequently.
Put the chicken back in the pan along with the wine and herbs. Bring to a simmer and cook for 3 minutes until reduced by half, then add the chopped tomatoes, stock and olives. Turn the heat to low, cover and simmer for 10 minutes. Stir in the rice and simmer for a further 10 minutes uncovered.
Meanwhile, see Notes for using shop bought basil pesto, or make the pesto by grinding the pine nuts, garlic, parmesan and chopped basil into a paste in a pestle and mortar (or pulse briefly in a small food processor). Stir in the oil, then taste and season with salt, pepper and a dash of lemon juice or cider vinegar.
Scatter the mozzarella over the rice, then cover and leave to gently cook for a final 5 minutes. Drizzle over the pesto, garnish with basil leaves and serve.