Heat the oil in a large casserole pot. Brown the chicken all over for 4 minutes on each side in two batches, until golden brown all over. Remove from the pan and set aside. Pour out any excess fat from the chicken into a small heatproof bowl and discard.
Add the onion to the pan and cook for 8 minutes, until golden and soft. Add the ginger, garlic, harissa and cumin and cook for 2 minutes, until fragrant. Add the carrot, parsnip and courgette and cook in the onion mixture for 1 minute, then add the rice, dates and stock. Mix well and season, then place the browned chicken on top, skin side up.
Simmer with the lid on for 25-30 minutes, until the vegetables are tender, the chicken is cooked through and the rice is cooked. Remove from the heat and stir everything through, then top with the chopped pistachio nuts.