Heat the tortilla on the pan. Turn the pan on to high heat and heat the tortilla or about a minute. Then flip the tortilla over and turn to medium heat. You shouldn't need any oil here, especially if you have a non-stick pan.
Crack the egg in a cup and whisk it with a fork. Sprinkle some cheese around the outer edge of the tortilla so that the egg doesn't spill over the edge, then pour the egg into the middle and spread around the tortilla with your spatula. Then place a lid on the pan and let your egg cook for about 3 - 5 min. It can help to put a couple drops of water on the surface of the pan (not on the tortilla) so that the steam helps to cook the egg.
Sprinkle leftover cheese and fold the tortilla. Once the egg is almost fully cooked, remove the lid and sprinkle the rest of the cheese on top. Fold the tortilla in half and cook for about half a minute on each side so the cheese is nicely melted inside.
Cut it up into triangles and serve with some fruit for breakfast or a cucumber, peppers and tomato salad for lunch.
Nutrition calculation is an estimate and will vary depending on the ingredients used. Not suitable for children under 1 due to sodium content equivalent to daily recommended intake (0.4g).