Heat 1 1/2 tablespoons of the oil in a large saucepan and gently cook the onion for 10 minutes, stirring frequently, until soft and translucent. Add the garlic, ginger, ground coriander, cumin and turmeric and cook for 2 minutes, stirring all the time.
Rinse the lentils, then stir them into the pan. Pour in the stock, bring to the boil, then reduce the heat, cover and leave to gently simmer for 10 minutes.
Meanwhile, heat the remaining oil in a frying pan and fry the cauliflower for 2–3 minutes until lightly browned. Add to the lentil mixture with the carrot and coconut milk.
Bring the curry to a gentle simmer and cook for a further 10 minutes, or until the vegetables are tender. Stir in the beans and cook for 3–4 minutes.
Stir in the chopped coriander and lemon juice, then season to taste with salt and freshly ground black pepper. Spoon onto a warmed serving dish or into four warmed serving dishes and garnish with extra coriander leaves.