Add the can of crushed tomatoes, ginger, turmeric, and sea salt to the pot and cook, stirring the pot a few times, for 5 minutes. Add the lentils and, if using, the cayenne or chilli powder, and the water to the pot and bring it to a boil. Reduce the heat to low, cover the pot, and let it simmer for 35-40 minutes, or until the lentils are soft. Stir the pot a few times to prevent the lentils from sticking to the bottom. If the curry starts to look dry, add an extra water. a tablespoon at a time.