2) Warm the oil over medium-high heat in a skillet, preferably cast iron. Add the seeds; they should sizzle upon contact. Once they stop popping, add the onions and saute until softened.
3) Add the mashed potatoes to the pan and flatten with a spatula so that the mash can begin to crisp. Continue to toss and re-flatten the potatoes until there are patches of crispy deliciousness all the way through the potatoes, about 10 minutes.
Remove from the heat, sprinkle with parsley, and serve.