In a large stock pot, heat oil over medium heat. Add the curry powder and toast for a few seconds, then add onion, garlic, jalapeno and coconut milk. Stir together and let cook 5 minutes.
Add lentils and water or stock. Bring to a boil, then turn the heat down and let simmer until lentils are tender, about 20-30 minute.
If desired, add yoghurt, tomatoes, cilantro and ginger. Adjust flavour with salt.