Preheat the oven to 200°C.
Place the sausages and onions into an ovenproof dish, drizzle with the vegetable oil and place in the oven until the sausages are cooked and the onions are soft. This should take about 20-25 minutes.
Make up the gravy if using instant, and prepare the Idahoan mash according to package instructions.
Pour the gravy over the sausages and onions, then top evenly with the mash, using a fork to create some texture.
Sprinkle with crispy onions the return to the oven for 10-15 minutes to brown the mash before serving.
