Heat the olive oil in a large Dutch oven over medium heat. Add the kielbasa slices and cook until lightly browned on both sides, about 5 minutes. Remove the sausage to a plate and set aside.
Add the sliced onions to the same pot. Cook, stirring often, until the onions soften and turn golden, about 8 minutes.
Return the kielbasa to the pot. Stir in the rinsed lentils, beer, chicken broth, bay leaves, salt, and black pepper.
Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for 30 to 35 minutes, stirring once or twice, until the lentils are tender but still hold their shape.
Remove the bay leaves before serving. Taste and adjust salt and pepper if needed.