Heat oil in a small frying pan over low to medium heat. Add onion, spinach, salt, and black pepper. Let it cook. When done, move the spinach mixture to the sides of the pan, and break one egg in the center. Mix well. Lower the heat, and let it cook slowly.

Meanwhile, whisk the other two eggs along with a pinch of salt until foamy. Set aside.

Transfer the spinach and egg mixture to a bowl. Set aside. Then, heat oil in the same pan over low heat, and pour in whisked egg. When one side is done, place spinach and egg mixture on one side of the omelette and fold it in half. Serve hot.