Crack the eggs into a small bowl and whisk until fully combined and slightly frothy, about 30 seconds.
Chop the spinach into bite-sized pieces and thinly slice the mushrooms, keeping them ready for cooking.
Heat your non-stick skillet over medium heat, then add a teaspoon of butter or oil, swirling to coat the pan evenly.
Add the sliced mushrooms to the hot pan and cook for 2-3 minutes, stirring occasionally, until they release a rich aroma and turn golden brown.
Stir in the chopped spinach and cook for about 1 minute until wilted and vibrant green, season with salt and pepper, then remove the mixture from the pan and set aside.
Pour the beaten eggs into the same skillet, tilting the pan to spread them evenly. Let cook undisturbed for about 1 minute until the edges start to set and a gentle shimmer appears on the surface.
Spread the sautéed mushrooms and spinach evenly over one half of the eggs. If using cheese, sprinkle it now for a gooey, melty effect.
Carefully fold the omelette in half with a spatula, pressing gently to seal the fillings inside. Cook for another 30 seconds to 1 minute until the center is just set but still moist.
Gently slide the omelette onto a plate, sprinkle with fresh herbs if desired, and serve hot to enjoy the tender, fluffy texture with earthy flavors.
