Slice the potato and onion into thin slices with a mandoline. Heat the oil over medium heat.
Once the oil is hot, add the potatoes and onions. Season with salt and pepper and cook until soft, but not brown. Don’t let the potatoes break when you stir them; remove them from the heat once this begins.
Beat the eggs with a pinch of salt and pepper in a separate container. Spoon in the potatoes and onions, stir, and re-add to the skillet (still at medium heat). Arrange the potatoes and onions so they lie flat.
After the edges firm up, lower the heat and cook for 5 minutes. Transfer the skillet to an oven at 375 degrees Fahrenheit and cook until the top is set, about 5-6 minutes.
Serve warm with salsa, arugula, greens, cheese, or whatever suits your fancy. Enjoy!