Heat oil over medium heat and add onions and scallion whites. Cook, stirring often, until golden brown and soft, about 10 minutes. Remove from heat and allow to cool.
If using regular yogurt, place it in a strainer lined with a paper towel and set the strainer over a bowl. Let the yogurt drain and thicken for 20 minutes.
Combine onions with thickened or Greek-style yogurt, mayonnaise, onion powder, garlic powder, salt, pepper and scallion greens and stir well to incorporate. Chill for 1 hour to let flavors meld. Serve with chips.