In 4-quart saucepan, heat 2 teaspoons oil over medium heat until hot. Add yellow onion; cook and stir about 4 minutes or until soft. Add cardamom and salt; cook and stir 30 seconds. Add lentils, tomatoes and water. Increase heat to medium-high; heat to boiling. Reduce heat to medium-low. Cover; cook about 30 minutes, stirring frequently, until lentils are soft and liquid is absorbed.