Preheat oven to 400ºF. In a large high-sided pan (preferably with a lid), heat oil over medium-high heat. Season the skin side of chicken with ½ tsp salt and place in the hot oil skin-side down and sear for 8 to 10 minutes, until chicken releases easily from the pan and skin is golden. Sear on the second side for 2 minutes and then transfer to a plate.
Reduce heat to medium and then stir in garam masala, cumin, turmeric and crushed red pepper flakes, stirring for 1 minute, until spices are fragrant and toasted. Stir in garlic followed by rice, raisins and broth. Squeeze over the juice of half of the lemon. Place chicken skin-side up on top of rice mixture; the chicken should be submerged in the broth with the skin visible.
Cover with lid or tight-fitting foil and bake for 45 minutes. Remove from oven, remove lid or foil and sprinkle over frozen peas and then transfer back to oven with the lid or foil off. Bake for another 5 minutes to lightly crisp up the chicken skin again and finish cooking the rice and peas. Slice the remaining lemon into wedges and use to decorate the top of the dish. Dollop over yogurt and sprinkle with cilantro and nigella seeds. Serve immediately.