In th bowl w/ set aside kielbasa, add Dijon mustard & toss to coat. Arrange kielbasa on top of onions in cooker. Spread sauerkraut, ( with any added ligiud reserved,) over kielbasa on top. Add reserved liquid. Cover & cook, on low for 4 hrs or until potatoes are tender. Sprinkle w/ 1 tbsp fresh, chopped thyme.