Toss the cut potatoes in olive oil, ¼ teaspoon salt, and ½ teaspoon garlic powder until all potatoes are well-coated.
Spread cut potatoes in an even layer onto a rimmed baking sheet lined with parchment paper or sprayed with cooking spray.
Roast the potatoes for 15 minutes. Remove from oven and use a spatula to stir, ensuring that that they are in a single layer when you finish stirring.
Return the potatoes to the oven and cook for another 15 minutes, or until potatoes are cooked through and many of them begin to brown. Remove from the oven to begin cooling.
Make the dressing by whisking together all of the dressing ingredients.
Stir together the potatoes, onions, celery, bacon, and dressing in a large mixing bowl. Chill before serving.