In a large pot, cover potatoes with water and season generously with salt.
Bring water to a boil and cook until potatoes are easily pierced with a knife, 15 to 20.
Drain and let cool slightly before transferring to a large serving bowl.
In a large skillet over medium heat, cook bacon until crispy, about 8.
Reserve about 2 tablespoons of fat in pan, and transfer bacon to a paper towel-lined plate to drain.
Add red onion and cook over medium heat until starting to soften, about 3.
Whisk in in apple cider vinegar, water, olive oil, dijon mustard, and sugar.
Bring mixture to a simmer, then turn off heat and season with salt and pepper.
Stir in green onions and gradually pour mixture over potatoes.
Toss to combine and serve warm.
