Chop the onion.
Grate the cheese.
Cut the chicken fillet.
Cut the potatoes.
Place the sliced potatoes in a deep bowl and add 2-3 tablespoons of mayonnaise, salt and pepper to taste. Mix thoroughly.
Place a layer of potatoes in a baking dish.
Place a layer of sliced chicken fillet on top of the potatoes.
Place a layer of chopped onions on the fillet.
Sprinkle the potato casserole with cheese.
Bake the potato casserole for 35-40 minutes. Place the finished dish on portioned plates and serve. Enjoy!