Heat oil in heavy medium saucepan over medium heat. Add onion and saute until soft, about 8 minutes. Add carrots and garlic and stir 2 minutes. Add lentils, then 2 cups of broth. Cover and simmer until lentils are just tender and broth is absorbed, uncovering at end if necessary to evaporate liquid, or adding more broth if too dry, 45 minutesto 1 hour. Mix in marjoram. Season to taste with salt & pepper