Set a large Dutch oven or heavy soup pot over medium heat.

Add the olive oil to the pot and let it heat for about 30 seconds.

Add the sliced kielbasa to the pot in an even layer. Cook for 3 to 4 minutes, stirring once or twice, until the sausage starts to brown.

Stir the sausage and cook for 2 to 3 minutes more, until there are browned edges on several pieces.

Transfer the browned sausage from the pot to a plate and leave the fat in the pot.

Add the chopped onion, diced carrots, and diced celery to the pot. Sprinkle in 1/2 teaspoon of the salt.

Cook the vegetables over medium heat for 5 to 6 minutes, stirring often, until the onion looks soft and the carrots begin to lose their raw look.

Add the sliced garlic to the pot. Cook for 30 seconds, stirring, until it smells fragrant.

Add the lentils to the pot and stir for about 30 seconds so they are coated with the oil and vegetable mixture.

Add the potatoes, broth, and bay leaf to the pot and stir once to combine.

Raise the heat to high and bring the liquid to a boil.

Lower the heat to medium-low so the stew bubbles gently. Partly cover the pot and cook for 18 minutes.