Season the chicken thighs with salt and pepper. Heat the olive oil in a large lidded ovenproof casserole dish over a medium-high heat. Add the chicken, skin-side down, and cook for 6-8 minutes until crisp.
While the chicken is browning, blend the spinach, peas, red peppers, vegetable stock cube and hot water in a blender or food processor and set aside.
Add the onion and ginger to the casserole dish and sauté, stirring regularly, for 5 minutes until softened.
Stir in the cumin, coriander, mustard seeds and chilli flakes and cook for another minute before adding the ground spices, prunes and the soaked rinsed lentils. Stir to coat the lentils in the spices before adding your blended peas, peppers and spinach mixture. Bring to a gentle simmer and cover with the lid. Cook for 15 minutes until the lentils are part-cooked, adding a splash more water if the mixture looks too dry.
Meanwhile, preheat the oven to 200°C fan.
Nestle the chicken, skin-side up, into the lentils, and cook, uncovered, in the oven for 20 minutes until the chicken is cooked through and the lentils are tender.
Serve with a drizzle of oil and sprinkled with coriander leaves.