Heat the oil in a large sauté pan, add the onion and cook for a few minutes until it softens. Add the ginger and garlic, chilli and continue to cook for a few minutes, taking care not to burn the garlic.
Add the spices, mix well and continue to cook for 1 minute. Add the lentils and stock, bring to the boil, reduce the heat, cover and simmer for 5 minutes. Add the sweet potato and red pepper. Cook for a further 20 minutes until the lentils and vegetables are cooked.
Season with salt and pepper and served sprinkled with the freshly chopped coriander.
Serve with rice or roasted cauliflower and raita and a nan bread on the side.