This meal has all the fun and salt of a wiener cookout, but it's a tiny bit fancier, and you can legit eat it in the winter.
Preheat the oven to 400.
Whisk together the mustard dressing ingredients and set aside. Chop parsley (optional).
Cut the kielbasa into thick coins and the potatoes into thick coins or small wedges. Mix them up with olive oil, salt, and pepper and spread them in a shallow pan.
Cut the cabbage into "steaks." Push the kielbasa and potatoes aside to make room to lay the cabbage down. Brush the cabbage with more olive oil and sprinkle with more salt and pepper. It should be a single layer of food, and not too crowded, so it will brown well.
Roast for 20 minutes, then turn the food as well as you can and roast for another 15 minutes.
Serve hot with dressing and parsley for a garnish.