Heat 1 tablespoon olive oil in a large saucepan over medium heat, stir in onion, garlic and salt; cook until the onion softened and translucent, about 4 minutes. Stir in lentils, and cook for 1 minute. Pour in water, then bring to a boil over high heat; turn heat to medium-low, cover, and simmer until the lentils are tender, about 15 minutes.