Preheat oven to 450F. Add quartered potatoes to a baking sheet and toss with oil and salt.
Roast potatoes at 450F for 10 minutes. Then add in the corn, tossing with the potatoes and place two pieces of bacon on one side of the pan.
Cook for another 15 minutes, until potatoes are tender and bacon is crispy. Remove from oven and let cool slightly.
While the potatoes are cooking, make the sauce. In a small bowl, mix together mustard, oil, apple cider vinegar, mayonnaise, garlic powder, salt and ground black pepper until combined. Set aside until ready to toss.
Place potatoes and corn in a large bowl. Crumble cooked bacon over the potatoes and add in chopped green onion.
Pour the sauce over the potato mixture and toss to coat. Serve at room temperature or chilled. Refrigerate until ready to use if not serving immediately. Keep leftovers in the refrigerator for 3-4 days.