Rinse the lentils well and bring to boil with water and bay leaf in a medium saucepan. Remove any foam that rises to the surface. When the water boils, reduce the heat to low, cover and simmer until the lentils are tender, 12 minutes. Add the salt.
Heat another saucepan over medium heat. When it’s hot, add the kielbasa. Brown it well on all sides, 10 minutes total. Remove the kielbasa from the heat.
Meanwhile, prepare the remaining ingredients. In the same pan that was used for the kielbasa, heat the olive oil over high heat. When it’s hot, add the diced carrots, finely diced onion, minced garlic cloves and marjoram. Season with a pinch of salt and pepper. Reduce the heat to medium and cook, stirring occasionally, until the vegetables are tender, 5 minutes.
Drain the lentils and add them to the pan with the vegetables. Stir in the kielbasa, vinegar, remaining olive oil and mustard. Take the pan off the heat and serve while hot.Enjoy Lentils With Kielbasa!