Place lentils and turmeric in a large saucepan; cover with 4 cups water. Bring to a boil; cover, reduce heat, and simmer 15 minutes, stirring occasionally. Add tomato; cook for 5 minutes or until lentils are tender. Stir in salt; keep warm.
Heat the vegetable oil in a small skillet over medium-high heat. Add cumin seeds and garlic; cook 2 minutes or until garlic is golden, stirring constantly. Stir in the red pepper, and remove from heat. Pour oil mixture over lentils, and stir in 2 tablespoons cilantro. Spoon the dal into individual bowls, and sprinkle with the remaining cilantro and the lemon juice.
This dal was OK -- not as good as Indian restaurant but an enjoyable side dish or lunch. As with some other reviewers, I used canned tomatoes, less water, and a bit more garlic. I pureed mine before serving so the consistency was closer to that of restaurant dal.