Toss together the chicken thighs oil, 1 tsp salt, garlic and lemon juice in a large bowl. Cover and chill for at least 1 hr, or up to 12 hrs.
Heat the oven to 180C/160C fan/gas 4, and heat a frying pan over a high heat. Fry the chicken, skin-side down, for 5-7 mins, or until golden and crisp. Transfer to a baking tray and sprinkle with the za’atar, then roast for 10 mins.
For the rice, heat the oil and butter in a large, shallow casserole or frying pan over a low-medium heat. Fry the onions with a pinch of salt for 15 mins until caramelised and sticky. Stir in the rice, stock, pistachios and chilli flakes. Season. Arrange the roasted chicken thighs on top of the rice, and pour over any roasting juices from the tray. Cook in the oven for 45 mins, or until the rice is tender. Remove from the oven, cover and rest for 5 mins.
Scatter the chicken pilaf with the pomegranate seeds and parsley, then serve in shallow bowls.