Preheat the oven to 400°F.
Place the potatoes in a pot and cover with water. Bring to a boil and cook until fork tender, about 15 to 18 minutes.
Arrange the bacon on a slotted broiler pan and place in the middle of the oven. Bake the bacon until crisp, 10 to 12 minutes. Cool, chop, and reserve.
Heat in a medium skillet over medium-high heat and add 2 tablespoons of olive oil. Add the red onion and sauté until just tender, about 5 minutes. Add the vinegar and stock and turn off the heat.
Preheat grill pan or a large nonstick skilled over medium-high heat. Drizzle the sliced kielbasa with a bit of olive oil and arrange on the preheated hot grill or in the preheated skillet. Cook for 2 minutes on each side, until hot and crisp on the edges.
Drain the potatoes and return to the hot pot. Fold the onion mixture inches Add the bacon, parsley, salt, and pepper. Drizzle in the remaining olive oil and add the cooked kielbasa.