Boil whole potatoes in salted water for 15–20 minutes until fork-tender.
Let potatoes cool slightly, then slice into rounds.
In a skillet, cook chopped chicken until crispy. Remove and set aside, leaving drippings in the pan.
Add chopped onion to the skillet and cook until soft.
Stir in vinegar, mustard, sugar, water, salt, and pepper; simmer for 2–3 minutes.
Add sliced potatoes to the skillet and gently toss to coat in the dressing.
Return chicken to the pan and mix well.
Sprinkle parsley on top and serve warm.