Clean the mushrooms with kitchen paper and slice them evenly. Rinse the fresh spinach and let it drain well so excess moisture doesn't end up in the pan later. Break the three eggs into a bowl and beat them vigorously with a fork.
Heat a generous amount of ghee in a frying pan over medium heat. Add the mushroom slices and brown them on all sides in a few minutes. Add the spinach in portions and briefly cook together until the leaves have just wilted.
Spread the vegetables evenly over the bottom of the pan and pour the beaten eggs over them. Lower the heat slightly and let the egg cook gently. Lift the edges occasionally with a spatula to allow the liquid egg to flow onto the hot bottom.
Fold the omelet in half with a spatula once the top is completely dry and cooked. Let the dish rest in the residual heat of the pan for half a minute and then slide it directly onto a plate.