Place the potatoes and onion in a bowl full of cold water. Soak for 5 minutes, drain, and fill again. Soak again for 5 minutes and drain. Continue rinsing and draining until the water no longer turns milky from the potato started.
Install the flat cooking plates on your Griddler and open the Griddler flat so you can cook on both plates at once.
Set your Griddler Selector to 'Griddle' and the Griddle temperature to 425 F.
Note that the top plate seems to not get as hot.
Drain potatoes well then toss with the oil, salt and pepper.
Divide the potatoes between the Griddler plates and spread out evenly.
Do not mess with the potatoes, let them cook for about 20 minutes or until you notice they are starting to turn golden brown on the bottom.Note that the top plate seems to not get as hot so the potatoes there may take longer to cook.
Carefully flip the potatoes and cook another 20 minutes or until they are nice and golden brown and are as crispy as you like them.
Serve hot with more salt and pepper, ketchup, or whatever you desire.