Heat the olive oil on medium high in a large pan, then add kielbasa and saute til kielbasa darkens and crisps up- about 7-10 minutes
With a slotted spoon remove kielbasa and set aside. Add butter and onions and saute til translucent- 2-4 minutes
Add the cabbage to the pan, reduce heat to medium, cover and saute for 5 minutes. Toss the cabbage and saute covered another 5 minutes.
Add the sausage, garlic and paprika back to the pan. Toss to combine, cover and saute another 5 minutes. Toss and saute another 5 minutes after.
Cabbage should be wilted and browning by now. Adjust seasoning with salt and pepper, serve with yellow mustard.