Prep ingredients: shred the cheese, slice the mushrooms and chop the onion.

In a bowl, crack the eggs and add a little salt and pepper to taste. Whisk with a fork until it is all mixed together and slightly frothy.

Melt the butter in a frying pan. Add the chopped red onion and sliced mushrooms to the pan. Season to taste, then cook until the mushrooms are tender, stirring occasionally. Pour in the egg mixture on top, making sure it gets between the onions and mushrooms.

When the omelet is starting to get done around the sides and on the bottom but still raw on top, sprinkle the cheddar cheese over the top.

With a spatula, get under the omelet carefully and fold it in half.

When the omelet is golden brown on the bottom, remove from the pan and serve hot.