Lightly toast the cumin and coriander seeds in a dry frying pan until you just start to smell their aroma, then grind them with a pestle and mortar.
Heat the oil in a large, heavy-based pan. Add the chicken pieces and fry over a high heat, turning once, until golden brown. (Don’t overcrowd the pan – cook in batches if you need to.) Transfer the chicken to a plate.
Add the onion