Heat oil in a large Dutch oven over medium heat until hot. Add lentils, onion, and chili powder; saute 2 minutes or until lentils are golden. Add potato and next 10 ingredients. Bring to a boil; reduce heat, and simmer, uncovered, 2 hours, stirring occasionally. Stir in salt and pepper. Remove and discard bay leaves. Ladle soup into individual bowls. Top each serving with 1 tablespoon yogurt.