Heat oil or lard to high temperature and saute onion until it gets a glassy / translucent look for about 3-5 minutes.
Add sliced kielbasa and garlic then saute until sausages are slightly seared for another 3 - 5 minutes. Fresh sausages will render out a good deal of fat at this stage.
Mix in the finely sliced cabbage and saute until it collapses somewhat for about 3 - 5 minutes.
Mix in vinegar, optional salt and pepper to taste. Stir fry on medium heat until some of the vinegar harshness disappears and the flavors come together nicely for another 3 - 5 minutes.