Wash the lenses under running water and then drain them.
Boil in a pan with 1 liter of water. Stir in salt, turmeric and 1/2 tsp. cayenne pepper and let the lentils simmer about 5 minutes, they should still have bite. Pour into a strainer and drain.
Peel potatoes and cut into cubes about 1 cm. Wash tomatoes, remove stalks and dice them. Peel onion, garlic and ginger, chop finely and mix.
Fry the onion mixture in oil. Add coriander, cumin, 1/2 tsp. of cayenne pepper and the curry paste. Stir in potatoes and tomatoes. Add 250 ml of water, boil up and simmer covered for about 15 minutes. Add the lentils and simmer for a further 5 minutes. Add some water if necessary.
Season with salt and cayenne pepper and fold in the chopped parsley.