Preheat oven to 425°F and line a large sheet pan with parchment paper.

Add peppers, garlic, onion, sauerkraut, and potatoes to the pan. Drizzle with olive oil, salt, and pepper. Toss to coat.

Bake for 15-18 minutes, or until the vegetables are tender.

While the vegetables are cooking, slice the kielbasa into ¼-inch slices, but not all the way through, using chopsticks or skewers to prevent cutting through completely.

Remove the sheet pan from the oven. Toss the veggies and nestle the kielbasa into them.

In a small bowl, combine mustard, apple cider vinegar, brown sugar, and Worcestershire sauce. Brush about ⅓ of the mixture over the kielbasa, reserving the rest for basting.

Transfer the pan back to the oven and bake for 40-45 minutes, or until the potatoes are fork-tender, basting with the mustard mixture every 10 minutes.

Garnish with parsley. Serve warm.