Bring a large pot of water to a boil. Add the diced potatoes and boil until tender, about 10 to 12 minutes.
Drain the potatoes and place in a large mixing bowl.
Place a cast-iron skillet over medium heat and once it is hot, add the bacon and cook it until crispy, about 7-8 minutes.
Remove bacon to a plate, leaving the grease in the pan.
Add red onion to the skillet and cook for 5 minutes, stirring, until soft.
Whisk in vinegar, olive oil, pickle juice, sugar, mustard, salt, and pepper, stir and cook for 1 to 2 minutes.
Pour the dressing over the potatoes, add bacon and parsley. Toss to combine.
Garnish with green onions.
Serve hot, or cold.