For the lentils: Soak the lentils in cold water for 2 hours. Drain. To the boiling water, add the lentils. Simmer, covered, for 15 to 20 minutes, adding more water if necessary For the rice: To the boiling water, add the salt and butter. Stir in the rice. Reduce heat and simmer, covered for 20 minutes. Remove from heat and let sit, covered, for 5 minutes. Remove lid and fluff with a fork. In a sautepan, cook onions in olive oil, then add rice and lentils and seasoning and more water if needed. Simmer approximately 10 minutes.