Heat the oil in a large pan, fry the onions for 5 mins until golden and softened, then tip onto a plate. Add the chicken breasts, browning for a few mins on each side, then stir in the balti paste, quinoa and onions. Sizzle for a few mins, then pour in the tomatoes and stock and give everything a good mix. Bubble for 25 mins until the quinoa is tender and saucy.
Stir in the cashews and most of the coriander with some seasoning, then pile into bowls and scatter over the rest of the coriander to serve.