Combine the lentils and 7 cups warm water in a pot, cover and bring to a boil. Add the chile pepper, tomato, ginger, garlic, turmeric and 2 teaspoons salt. Partially cover and simmer over medium-low heat, stirring frequently, until thickened, 18 to 20 minutes. Stir in the cilantro. Thin the soup with water, if desired, and season with salt.
Mix the yogurt with 2 teaspoons water and a pinch of salt in a small bowl. Ladle the soup into bowls and top with the yogurt and more cilantro. Serve with naan.