Rinse the lentils several times until the water runs clear, then tip into a saucepan with 1 litre water and a pinch of salt. Bring to the boil, then reduce the heat and simmer for 25 mins, skimming the froth from the top. Cover with a lid and cook for a further 40 mins, stirring occasionally, until it’s a thick, soupy consistency.
While the lentils are cooking, heat the ghee or oil in a non-stick frying pan over a medium heat, then fry the onion and garlic until the onion is softened, so around 8 mins. Add the turmeric and garam masala, then cook for a further minute. Set aside.
Tip the lentils into bowls and spoon half the onion mixture on top. Top with the coriander and tomato to serve.