In a large skillet, heat the extra virgin olive oil over low-medium heat.
Add the sliced kielbasa to the skillet. Cook for about 4 minutes on each side, stirring occasionally, until the sausage starts to brown. Transfer the kielbasa to a plate and set aside.
In the same skillet, add the sliced red onion. Cook for about 2-3 minutes until softened and slightly caramelized.
Sprinkle the brown sugar over the onions and stir to combine. Cook for another 2-3 minutes until the sugar starts to melt and the onions become even more caramelized. Transfer the onion to a small bowl and set aside.
Add the sauerkraut to the skillet, season with black pepper and Dijon mustard, stirring well. Let it cook for 2 minutes to warm through.
Return the cooked kielbasa to the skillet and caramelized onion, mixing everything together so the flavors meld. Cook for another 1 minute until the mixture is heated through.
Sprinkle with fresh parsley before serving.
Notes
Sear the Kielbasa: Brown the kielbasa over medium heat to bring out its flavor without burning. Take your time, let each piece brown evenly for that perfect crisp.Sweet & Savory with Brown Sugar: Brown sugar balances the tangy sauerkraut and sweetens the onions. Adjust to your taste, a little extra for more sweetness, or less if you prefer it sharper.Caramelize the Onions: Cook the onions slowly with brown sugar to build a deep, caramel flavor. It takes a few minutes, but the rich sweetness is worth it!Make Ahead: This dish tastes even better the next day as the flavors meld. Store in the fridge for up to 3 days, and reheat gently on the stove.Storage: Keep leftovers in an airtight container in the fridge for 3–4 days.