Heat the oil in a pot over medium high heat and cook the onions until soft and translucent, 5-7 minutes. Add the carrots, garlic and leek and continue cooking another 5 minutes. Add the curry powder and cook for another minute. Add the tomatoes, lentils, bay leaf, salt, pepper and broth. Bring everything to a boil then reduce the heat to medium, cover, and simmer for 25-30 minutes or until the lentils are soft. Stir in the cilantro and add salt and pepper to taste. Serve hot garnished with some chopped cilantro.