In a non-stick skillet, heat 1 teaspoon of olive oil over medium heat. Add the minced garlic and sliced mushrooms. Sauté for about 5-7 minutes, or until the mushrooms are tender and have released their moisture. Stir in the minced parsley and season with salt and pepper to taste. Remove from heat and set aside.
In a mixing bowl, separate the egg whites from the yolks. Put the yolks in one bowl and the whites in another. Whisk the yolks until they are light and frothy.
Using a whisk or electric mixer, beat the egg whites until they form stiff peaks. This step is crucial for achieving that soufflé-like fluffiness.
Gently fold the beaten egg whites into the yolk mixture, being careful not to deflate the whites. Once combined, carefully fold in the sautéed mushrooms and cheddar cheese.
Wipe down the skillet and return it to medium-low heat. Pour the omelette mixture into the skillet, spreading it evenly. Cover with a lid and cook for about 5-7 minutes, or until the bottom is set and the top is slightly wobbly.
Once the omelette is cooked through, carefully slide it onto a plate. You can fold it in half or serve it flat. Garnish with additional parsley if desired, and enjoy your light and fluffy Souffle Omelette with Mushrooms!