In a small bowl or jar, combine olive oil, red wine vinegar, mustard, garlic powder, and a pinch of salt and pepper. Whisk or shake until well emulsified and creamy. Set aside.

Heat a large skillet over medium heat and add the sliced kielbasa. Sauté for 5-7 minutes or until evenly browned and caramelized.

Add 1 diced onion to the skillet with the kielbasa and cook for about 5 minutes, stirring frequently until soft and translucent.

Stir in chopped cabbage along with a pinch of salt and pepper. Cook for approximately 8-10 minutes, stirring occasionally until tender.

Drizzle half of the mustard vinaigrette over the skillet mixture and gently stir to coat evenly.

Remove from heat and garnish with fresh parsley or dill. Serve warm.