Wash the chicken, pat dry and cut into 1 1/2 cm cubes. Rinse the lentils in a sieve under cold running water until the water runs off clear and let them drain.
Peel the onion, garlic and ginger, finely chop everything. Melt the ghee in a saucepan and fry the onion until golden brown. Add the garlic, ginger and the chicken cubes, sprinkle with cumin, coriander, curry and cayenne pepper and stir-fry for about 30 seconds.
Add the lentils and the broth, season with salt if necessary. Bring everything to the boil, cover and simmer over low heat for about 30 minutes until the lentils are cooked through.
Pour in the coconut milk and simmer the soup for another 5 minutes. Season to taste with lemon juice and serve garnished with coriander leaves if you like.