Preheat the oven to 200°C/400°F/gas 6. Peel and chop the potato into 2.5cm cubes. Cook in boiling salted water for 6 minutes, then drain well and steam dry. Add the turmeric and cumin to a bowl, then grate in half the lemon zest. Pick, roughly chop and add the coriander leaves. Deseed and roughly chop the pepper and peel and matchstick the ginger, then add to the bowl. Cut 2 slices of lemon and set aside. Squeeze a little juice from the remainder of the lemon into the bowl. Shake the potatoes up in the colander and add them to the bowl, along with the chicken. Drizzle with oil and season with sea salt and black pepper, then toss everything around to coat. Remove the chicken from the bowl, then tip the potato mixture into a baking dish (roughly 10cm x 15cm) and spread out into a single layer. Top with the lemon slices, then drape over the chicken. Drizzle with oil, then cook in the middle of the oven for 25 minutes, or until golden and cooked through.