Heat the oil in a large heavy frypan and add the onion and garlic. Cook, stirring, until onion is browned. Add the chicken and chorizo and cook until the chicken is opaque and chorizo has released its oils. Add the chilli flakes and cook 1 more minute.
Add the rice and stir over medium heat until coated with the oil. Add the wine and stir well. Begin adding the stock, a little at a time and stirring constantly.
Keep adding stock and stirring for about 20 minutes, then add the peas and cook 5 more minutes, adding more stock if necessary. Keep cooking until the liquid is absorbed and the rice is creamy with a little bite still to it.
Just before serving, add the mascarpone and Parmesan and stir well.