In a large skillet, heat the olive oil over medium heat. Once it's hot, add the onion and cook, stirring often, until it is softened and translucent. Then add the beaten egg to the pan. Cook and stir until the eggs are softly set, then add the spinach to the pan. Continue to cook and stir to wilt the spinach down.

Add the leftover rice to the skillet along with the soy sauce and sesame oil. Cook and stir around for another couple of minutes to heat the rice through and toast it slightly, then remove the pan from the heat and serve.