Heat the oil in a big soup pot over a medium heat. Add the onion and cook until softened, about 10 minutes. Add the garlic, ginger, curry powder and chilli flakes and cook for another couple of minutes.
Add the lentils to the pot and stir to coat in the spices them pour in the tomatoes, chopped coriander, 500ml of water, coconut milk (keeping back a couple of tablespoons for serving if desired) and plenty of salt and pepper.
Bring the soup to a simmer and cook for about 20 minutes until the lentils are tender. Serve drizzled with the leftover coconut milk, coriander leaves, Greek yoghurt and lime wedges.
Nutrition information is an estimate and will vary depending on the ingredients used.