Chop the onion and sauté in a little oil, add the tomato paste and sauté.
Add the canned lentils with their juice, possibly add a little water.
Add a dash of vinegar and season with salt, pepper and marjoram. Let it simmer for a while and finally add the sliced sausages.
If the lentil stew is too liquid, thicken with a little flour or cornstarch.