In a large pot, cover the halved potatoes with water and season generously with salt. Bring the water to a boil and cook until the potatoes are easily pierced with a knife, about 15 to 20 minutes. Drain and let them cool slightly before transferring to a large serving bowl.

In a large skillet over medium heat, cook the bacon slices until they are crispy, approximately 8 minutes. Reserve about 2 Tbsp of the drippings in the pan and transfer the cooked bacon to a paper towel-lined plate to drain.

Add the chopped red onion to the skillet and sauté over medium heat until it starts to soften, about 3 minutes.

Whisk in the apple cider vinegar, water, olive oil, Dijon mustard, and sugar. Bring the mixture to a simmer, then remove from heat and season with salt and pepper.

Stir in the green onions and gradually pour the dressing over the warm potatoes. Crumble the crispy bacon on top.

Toss everything gently to combine and serve warm.